Include guidance on sharing content (#2117)

* Include guidance on sharing content

* Apply suggestions from code review

Co-authored-by: Sam <sam@writethedocs.org>

* Apply suggestions from code review

* Wording suggestions

* Fix link

* Update docs/slack.rst

Co-authored-by: Daniel D. Beck <daniel@ddbeck.com>

* spellcheck begone

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Co-authored-by: Sam <sam@writethedocs.org>
Co-authored-by: Janine Chan <64388808+janine-c@users.noreply.github.com>
Co-authored-by: Sam Wright <samuel@plaindocs.com>
Co-authored-by: Daniel D. Beck <daniel@ddbeck.com>

docs/slack.rst

@@ -234,6 +234,10 @@ Please be mindful with the following behaviors:
 - **Avoid technology competitions.**
   It doesn't matter if your tool is faster or better in some metric.
   We care about creating great documentation for our users.
+- **Honor the community's trust and confidence.**
+  In the Write the Docs Slack, we are privileged to be able to discuss complex or sensitive situations with other docs practitioners.
+  But those discussions can only happen in an environment of discretion and trust.
+  The Chatham House Rule <https://www.chathamhouse.org/about-us/chatham-house-rule>`_ applies: you're welcome to use the information shared, but never reveal names, job titles, employers, or other identifying information about other participants outside of Slack, unless you've received their explicit permission to do so.
 
 Posting rules
 ~~~~~~~~~~~~~