doc: Reorganization

[crandmck]

Changes in this pull request

Create new docs directory and move some content from README to new files there:

• release-notes.md - Release notes, including info on new API that's currently in 2024_API_NOTES.md
• usage.md - Docs on using the library. Currently minimal, will expand in future.
• supported-formats.md - Table of supported media file formats. Having this in a separate file makes it easier to "transclude" it into docs for other libraries (noting any diffs).
• project-contributions.md - Info for anyone who wants to contribute to (vs. use) the crate, including testing info.

For details, see https://wiki.corp.adobe.com/display/CAI/Rust+library+docs.

Checklist

• [x] This PR represents a single feature, fix, or change.
• [x] All applicable changes have been documented.
• [x] Any TO DO items (or similar) have been entered as GitHub issues and the link to that issue has been included in a comment.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 81.52%. Comparing base (2a41ee5) to head (ae56e3c).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #689 +/- ## ======================================= Coverage 81.52% 81.52% ======================================= Files 104 104 Lines 30614 30614 ======================================= Hits 24958 24958 Misses 5656 5656 ```

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