chore: update readmes

[Bento007]

Reason for Change

• add release process for ontology assets, api, and descendant mappings

Changes

• add description and release process for ontology assets, api and descendant mappings
• rename artifact-schemas -> asset-schemas
• added license badge to readmes
• update shield tags to links to related resource
• update the API documentation to include badges and it's own description

[codecov[bot]]

Codecov Report

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

Project coverage is 85.29%. Comparing base (e9a4ab5) to head (389cd2c).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #171 +/- ## ======================================= Coverage 85.29% 85.29% ======================================= Files 19 19 Lines 1095 1095 Branches 210 210 ======================================= Hits 934 934 Misses 151 151 Partials 10 10 ``` | [Flag](https://app.codecov.io/gh/chanzuckerberg/cellxgene-ontology-guide/pull/171/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=chanzuckerberg) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/chanzuckerberg/cellxgene-ontology-guide/pull/171/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=chanzuckerberg) | `85.29% <100.00%> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=chanzuckerberg#carryforward-flags-in-the-pull-request-comment) to find out more.

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