[doc]: Document version-tagging specification

[dstadulis]

Is your feature request related to a problem? Please describe.
Problem:
As a taproot-asset protocol developer I would like to have a document specifying the git tag standard in order to ensure that tags are conformant to various downstream needs such as the version-checking script and regex matches. This specification would be in addition to https://semver.org/
[edit] @ffranr found this helpful site, as referenced in #720
https://jubianchi.github.io/semver-check/#/version/0.3.2-alpha.2

It would be helpful to avoid mistakes or reloading all the context and requirements each time a release is performed and instead document the requirements.

Describe the solution you'd like
A document, added to the repo, specifying what the required form of git tags are to use for:

• Releases
• Release candidates
• Alternative releases

Describe alternatives you've considered
Not documenting the standard and spending time each release recalling them.

[ffranr]

Closed in favour of #729