Add deprecation guidelines to CONTRIBUTING.md

[Isurunwg]

Proposed changes

This PR adds a Deprecation Guidelines section to the CONTRIBUTING.md file. The new section introduces a standardized template for documenting deprecated methods, classes or functionalities.

Types of changes

What types of changes does your code introduce to this project?
Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of
them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before
merging your code.

• I have read the CONTRIBUTING.md
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

This change was made to address a request for standardizing the deprecation documentation process. If there are additional suggestions or adjustments required, I’d be happy to update the PR accordingly.

[OneLiteFeather]

LGTM