Create CONTRIBUTING.md

This commit adds the contributing guidelines for creating
the changelog entries. This is needed to start using the
https://github.com/Bitergia/release-tools for generating
releases for the GrimoireLab Toolkit.

Signed-off-by: Venu Vardhan Reddy Tekula <venu@bitergia.com>

CONTRIBUTING.md

@@ -0,0 +1,110 @@
+# Contributing to GrimoireLab Toolkit
+
+These are some general guidelines and information related to how we contribute to 
+GrimoireLab. You can read about it from the [CONTRIBUTING.md](https://github.com/chaoss/grimoirelab/blob/master/CONTRIBUTING.md).
+
+## Changelog Entries
+
+Some of your contributions will require a changelog entry which explains 
+the motivation of the change. These entries would be included in the 
+release notes to explain users and developers about the new features 
+or bugs fixed in the software. This is an example of changelog entry:
+
+```
+title: 'Fix bug casting spells on magicians'
+category: fixed
+author: John Smith <jsmith@example.com>
+issue: 666
+notes: >
+    The bug was making impossible to cast a spell on
+    a magician.
+```
+
+Changelog entries will be written to explain *what* was changed and *why*, 
+not *how*. Take into account not everybody is a developer and they are 
+meant to reach a wider audience.
+
+### What warrants a changelog entry
+
+Changelog entries are **required** for:
+- Code changes that directly affects the GrimoireLab users.
+- Bug fixes.
+- New updates.
+- Performance improvements.
+
+Changelog entries are **not required** for
+- Docs-only (e.g., README.md) changes.
+- Developer-facing change (e.g., test suite changes).
+- Code refactoring.
+
+### Writing changelog entries
+
+These changelog entries should be written to the `releases/unreleased/` 
+directory. The file is expected to be a [YAML](https://yaml.org/) file 
+in the following format: 
+
+```
+title: 'Fix bug casting spells on magicians'
+category: fixed
+author: John Smith <jsmith@example.com>
+issue: 666
+notes: >
+    The bug was making impossible to cast a spell on
+    a magician.
+```
+
+The `title` field has the name of the change. This is a mandatory field.
+
+The `category` field maps the category of the change, valid options are: 
+added, fixed, changed, deprecated, removed, security, performance, other. 
+This field is mandatory.
+
+The `author` key (format: `Your Name <YourName@example.org>`) is used to 
+give attribution to community contributors. This is an optional field but 
+the Community contributors are encouraged to add their names.
+
+The `issue` value is a reference to the issue, if any, that is targeted 
+with this change. This is an optional field.
+
+The `notes` field should have a description explaining the changes in the 
+code. Remember you can write blocks of text using the `>` character at the 
+beginning of each block. See the above given example.
+
+Contributors can use the interactive [changelog](https://github.com/Bitergia/release-tools#changelog)
+tool for this purpose which generates the changelog entry file automatically.
+
+### Tips for writing good changelog entries
+
+A good changelog entry should be descriptive and concise. It should explain 
+the change to a reader who has *zero context* about the change. If you have 
+trouble making it both concise and descriptive, err on the side of descriptive.
+
+Use your best judgment and try to put yourself in the mindset of someone 
+reading the compiled changelog. Does this entry add value? Does it offer 
+context about *what* and *why* the change was made?
+
+#### Examples
+
+- **Bad:** Go to a project order.
+- **Good:** Show a user’s starred projects at the top of the “Go to project” dropdown. 
+
+The first example provides no context of where the change was made, or why, or 
+how it benefits the user. 
+
+- **Bad:** Copy (some text) to clipboard.
+- **Good:** Update the “Copy to clipboard” tooltip to indicate what’s being copied. 
+
+Again, the first example is too vague and provides no context.
+
+- **Bad:** Fixes and Improves CSS and HTML problems in mini pipeline graph and builds dropdown.
+- **Good:** Fix tooltips and hover states in mini pipeline graph and builds dropdown. 
+
+The first example is too focused on implementation details. The user doesn’t care 
+that we changed CSS and HTML, they care about the result of those changes.
+
+- **Bad:** Strip out `nil`s in the Array of Commit objects returned from `find_commits_by_message_with_elastic`
+- **Good:** Fix 500 errors caused by Elasticsearch results referencing garbage-collected commits 
+
+The first example focuses on *how* we fixed something, not on *what* it fixes. 
+The rewritten version clearly describes the *end benefit* to the user 
+(fewer 500 errors), and *when* (searching commits with Elasticsearch).