Make location of "Release Checklist" source obvious

[pljones]

Short description of changes

Old text:

• Update this template in https://jamulus.io/contribute/Release-Process with any improvements if needed.

This does not tell the reader where to go to find the actual thing they need to change, hence it's a layer of obfuscation rather than help.

New text:

• If needed, make any improvements to the "Release Checklist" in the source of this document.

The link now goes directly to the source in the website repository

Context: Fixes an issue? Related issues

Fixes 1128

Status of this Pull Request

Wording as above.

What is missing until this pull request can be merged?

Needs review.

Does this need translation?

Yes.

Checklist

• I've verified that this Pull Request follows the general code principles
• I waited some time after this Pull Request was opened and all GitHub checks completed without errors.
• I'm sure that this Pull Request goes to the correct branch