Feature: Add examples of mixed JS-and-TS linting

[JoshuaKGoldberg]

Coming from typescript-eslint/typescript-eslint#8777: it'd be nice to show examples of using us in projects that also have .js/.jsx/etc. files.

• Both using typed linting in JS (i.e. // @ts-nocheck) and disabling it
• For typed linting with a jsconfig.json and without (just defaulting to the tsconfig.json)