Docs: contributing docs should say how to update rule doc code example snapshots about typescript-eslint

[auvred]

I'm +1 on adding some docs about snapshots and how to deal with them! In addition to ESLint output snapshots, we have rule schema snapshots. It would be nice to mention them as well.

https://github.com/typescript-eslint/typescript-eslint/tree/4858afde147a5ff6fa20ac1e73bc1c04692cef7a/packages/eslint-plugin/tests/schema-snapshots

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Btw, we can also explain how to work with ast-spec snapshots. This may seem non-trivial!
There is a great explanation from Brad: #7649 (comment) 👍

• within this folder create a folder called fixtures.

• within fixtures create a _error_ folder

• within _error_ create a folder with a name for your case - for example maybe using-initializer?

• within that folder, create a file called fixture.ts

• within that file add your test code (eg for(using foo in {});)

• cd packages/ast-spec && yarn test to run the fixture tests and generate the necessary snapshots.

[JoshuaKGoldberg]

Yeah I cd eslint-plugin; yarn test schemas -u to update snapshots. +1 to docs