Documentation updates after 1.0.0 Trial Use Review Ballot

[brendanreardon]

This is a running list of recommended documentation updates that we should make in response to the 1.0.0 Trial Use Review Ballot (November 2024) feedback.

A non-exhaustive list of these changes to do are:

• Add Python reference implementation, from @korikuzma
• Broaden description of Categorical Variant class, from @rhdolin [commit]
• The Discussions section of CONTRIBUTING.md describes recommendations for creating Issues, instead of Discussions [commit]
• Expand upon concepts documentation within docs/source/concepts/.

[brendanreardon]

These changes are being addressed in branch 91-documentation-updates-post-ballot.

[brendanreardon]

I also noticed that the style guide link is broken within the contributing document, but it is present in docs/tobedeleted/. Did we want to update this link to just point to the style guide within the VRS repo?