[DOC]- Update contribution guidelines

[trallard]

Fixes #1078

Changes:

• Removes references to main
• Adds more details on how to contribute
• Adds extra --- to RELEASE.md to make it easier to read

Types of changes

What types of changes does your code introduce?

Put an x in the boxes that apply

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds a feature)
• Breaking change (fix or feature that would cause existing features to not work as expected)
• Documentation Update
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build related changes
• Other (please describe):

Testing

Requires testing

• Yes
• No

In case you checked yes, did you write tests?

• Yes
• No

Further comments (optional)

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered and more.

[costrouc]

@trallard looks great to me. Vale checks are a little too strict