docs: Add link to contributing to docs

[catmsred]

On the page for contributing to the docs, there is no direct link to the docs source code. This change adds a link to the top of that page.

Proposed Commit Message

docs: Add link to contributing to docs
    
On the page for contributing to the docs, there is no direct link
to the docs source code.  This change adds a link to the top of
that page.

Checklist

• My code follows the process laid out in the documentation
• I have updated or added any unit tests accordingly
• I have updated or added any documentation accordingly

Merge type

• Squash merge using "Proposed Commit Message"
• Rebase and merge unique commits. Requires commit messages per-commit each referencing the pull request number (#<PR_NUM>)

[TheRealFalcon]

LGTM!