1361 Changelog Addition

[ACStone-MTS]

What does this PR fix/introduce?

This PR establishes a CHANGELOG.md for the docs repo, as well as a version available on the actual documentation site that allows for quick reference of changes made during protocol releases.

Closes #1361

Additional context

Establish a Change Log for the Docs #1361

Checklist

(Delete any that aren't relevant)

• Docs are successfully building - yarn install && yarn run build.
• For new internal links I used relative file paths (with .md extension) - e.g. ../../faq/faq-general.md - instead of introducing absolute file path, or relative/absolute URL.
• My changes follow the Casper docs style guidelines.
• If structural changes are introduced (not just content changes), cross-broswer testing has been completed.

Reviewers

@ipopescu

[ACStone-MTS]

Build error will be fixed by #1360, so I'll wait for that one to merge before merging this one to avoid any additional conflicts.

[ipopescu]

This is very helpful! Recommending a single link in the CHANGELOG.md file.