glob actions need better documentation

Glob actions are referenced for pattern matching throughout the actions (like https://github.com/marketplace/actions/upload-a-build-artifact) but the docs don't explain how the pattern engine works. There's no guidance on how it should work and even the tests are underwhelming in providing documentation on how it should work.

If this is using ANY regex engine or other engine leveraged from nodejs or other thing, please SAY SO and point to the docs of that engine. If those docs don't exist one needs to be written. Right now, it's really hard to understand how pattern matching should work, and this is a very useful feature, specially in workflows that uses multiple OSes and environments in their strategy/matrix.

Start with the packages/glob entry point and read packages/glob/tests/internal-pattern.test.ts to determine how pattern matching currently works. Document the engine or Node.js facility used, explain its behavior for cross-platform workflows, link to authoritative engine documentation, and ensure the tests and documentation describe the same behavior.