New pattern: Cross-Team Retrospectives (#691)

* Adds a new pattern at initial state that recommends running regular cross team retrospectives in particular for long running collaborations between host team and a stable set of contributors.

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Co-authored-by: Sebastian Spier <github@spier.hu>

README.md

@@ -85,6 +85,7 @@ Our mission
 * [InnerSource Customer Interview Questions](/patterns/1-initial/innersource-customer-interview-questions.md) - *An organization has decided to create an InnerSource program but are unsure which issues they should address first. Using a customer interview will help evaluate pain points across the organization, to prioritize the areas where InnerSource will have the biggest positive impact.*
 * [Creating an InnerSource Strategy](/patterns/1-initial/creating_an_innersource_strategy.md) - *Sometimes, it is difficult to convince people of the relevance of InnerSource for your organization and/or to get support from management. Creating an InnerSource strategy, that connects your InnerSource approach and activities to the goals and the overall strategy of your organization, can help in this regard.*
 * [Code of Conduct](/patterns/1-initial/code-of-conduct.md) - *Communications and interactions between collaborators are rude, not inclusive or offensive, harming and increasing the discussions without any value added. A Code of Conduct provides guidelines for establishing rules and expectations regarding behavior and interactions within the community to build stronger levels of collaboration.*
+* [Trusted Committer and Contributor Retrospectives](/patterns/1-initial/cross-team-retrospectives.md) - *A host team working with contributors outside of their own line of management constantly runs into misunderstandings. As a result collaboration becomes brittle and frustrating. Setting aside time for regular retrospectives for the InnerSource team consisting of trusted committers and contributors can help make communication smooth.*
 
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 NOTE: The 'Initial' Patterns below don't have a Patlet yet, which is essential for readers to quickly browse our patterns.

patterns/1-initial/cross-team-retrospectives.md

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+## Title
+
+Trusted Committer and Contributor Retrospectives
+
+## Patlet
+
+A host team working with contributors outside of their own line of management constantly runs into misunderstandings.
+As a result collaboration becomes brittle and frustrating.
+Setting aside time for regular retrospectives for the InnerSource team consisting of trusted committers and contributors can help make communication smooth.
+
+## Problem
+
+For long running collaborations friction between host team and collaborators is substantially reducing focus and energy for everyone involved.
+Willingness to continue the collaboration is shrinking.
+
+## Context
+
+A host team of [trusted committers](../2-structured/trusted-committer.md) has started a long running collaboration with a group of contributors.
+
+* Over time the number of misunderstandings grows.
+* People may run into mis-communication.
+* Teams may discover slight differences in development culture.
+* Team members may discover that assumptions they made about how the other team works are false.
+* Contribution processes may not be entirely clear and workable for everyone involved.
+
+## Forces
+
+* Participants are inclined to take "written over verbal" as "only written".
+* Trusted committers are all part of the same team.
+* There is a group of contributors all coming from the same team.
+* As a result trusted committers know each other well and understand constraints, prioritization side effects and team dynamics without ever sharing them with contributors.
+* Also contributors form a well knit group.
+* The contribution process is seen as transient and temporary.
+As a result little is invested in forming a shared team of trusted committers and contributors.
+* There is no clear path from contributor to becoming trusted committer - other than becoming a member of the host team.
+
+## Solution
+
+Bring host team and contributors together:
+
+* As a first step it can help to share a meal together and get to know each other.
+* For collaborations running over several weeks establish a monthly retrospective meeting that involves everyone who is needed for a successful contribution.
+* Make sure that action items for each restrospective are being followed up upon, ideally check these action items at the beginning of the next retrospective.
+* Keep the agenda of retrospectives stable and predictable: It's already uncomfortable enough to name and resolve collaboration issues.
+
+Example agenda:
+
+* 5 minute check-in so everyone can test their audio setup, silly questions preferred so people can laugh together, reducing overall stress.
+* 5 minute review for action items from last meeting (each item presented by its owner)
+* 10 minutes to gather strengths and weaknesses of the past collaboration time period. Do this as a combination of writing (sticky notes on a digital white board) and verbally explaining the stickies to make sure introverts get involved as well.
+* 2 minutes to put dots against weaknesses that should be addressed in the next cycle. Pick the top 1-2 weaknesses.
+* 10 minutes to gather potential remedy actions to address the picked weaknesses. Again use time for writing sticky notes to involve everyone.
+* 2 minutes to put dots against action items (each participant may add 2-3 dots), pick at most top 3 items, assign each item two owners - one trusted committers and one contributor.
+* 5 minutes for checkout so everyone can wind down and leave feedback on the meeting.
+
+Caveat: In particular for cases where people have tried to collaborate for a long time already, the initial meeting may need more than 30 minutes.
+
+## Resulting Context
+
+* Trusted committers understand how to improve communication and contribution processes.
+* Contributors understand how to support trusted committers in improving documentation and processes.
+* Likely both uncover issues that are beyond their direct control but also see ways to address these in the organisation adopting InnerSource.
+* Ideally several learnings can be shared with other InnerSource teams so they avoid running into the same trouble.
+* When done regularly after a handful of retrospectives collaboration improves, issues uncovered reduce, turning the session more and more into a lot of positive feedback. As a result motivation on both sides increases.
+* [Communication Tooling](../2-structured/communication-tooling.md) and [Base Documentation](../2-structured/base-documentation.md) improves.
+
+## Related material
+
+* [Generator for check-in questions](https://www.checkin-generator.de) (in German)
+* [Examples of retrospective formats](https://retromat.org/en/)
+
+## Known Instances
+
+* Europace AG
+
+## Status
+
+Initial