Document typescript as supported language for syntax highlighting

[mportiz08]

Bug/issue #, if applicable:

Summary

Document that typescript code listings can now be syntax highlighted with DocC-Render.

Adds an entry to the "Add Code Listings" section of "Formatting your documentation content" that documents which languages are expected to have syntax highlighting support in the renderer.

Dependencies

swiftlang/swift-docc-render#975 (thanks @mgrebenets)

Testing

Steps:

1. Run bin/preview-docs DocC and verify that the table at http://localhost:8080/documentation/docc/formatting-your-documentation-content#Add-Code-Listings has a new entry for typescript

Checklist

Make sure you check off the following items. If they cannot be completed, provide a reason.

• Added tests
• Ran the ./bin/test script and it succeeded
• Updated documentation if necessary

[mportiz08]

@swift-ci test

[heckj]

nice!