Contributing: Update style guide

These are from the heading "Contributing to OCDS". There are comments on some of these points in the document.

Note that the handbook has changed a bit since then.

Style guide

Currently guidance is divided into several parts with different levels of importance and consistent usage across the sections.

[ ] Consider - Creating a unified style guide “checklist” for contributors to review before making new contributions to OCDS to ensure that policies are applied consistently across contributors.
[ ] Consider - ~~Combining this page with the Handbook style guide and~~ expanding guidance offered to be more detailed for contributors.
[ ] Consider - Adding guidance around page hierarchy in OCDS.

As noted above, the use of admonitions is inconsistent across the OCDS, with a variety of terms and formats used interchangeably.

[ ] Consider - Compiling all uses of admonitions in one place to compare/contrast formats and purpose of the admonition.
- Bloom's taxonomy can be a useful orientation for the admonitions and learning objectives (I think we have admonitions for "Remember", "Understand", "Apply"). That said, in some cases, admonitions are not related to learning, like invitations to contribute to a GitHub issue, or a note about the version in which something changed. Still, the taxonomy generally orients toward using verbs, which can be applied outside of learning objectives (using "Contribute" for the Github example).
[ ] Consider - Using one color admonition (I recommend green) for examples throughout OCDS.