docs: Add Typescript instructions to Contributing guide

[dplewis]

Pull Request

• Report security issues confidentially.
• Any contribution is under this license.
• Link this pull request to an issue.

Issue

Typescript instructions are missing.

Ref: #2012

Approach

• Properly document how to build and test type definitions

Tasks

• Add tests
• Add changes to documentation (guides, repository pages, code comments)

[parse-github-assistant]

Thanks for opening this pull request!

• ❌ Please link an issue that describes the reason for this pull request, otherwise your pull request will be closed. Make sure to write it as Closes: #123 in the PR description, so I can recognize it.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (e6dc1b5) to head (dc8d025).

Additional details and impacted files

@@            Coverage Diff            @@
##             alpha     #2463   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           64        64           
  Lines         6259      6259           
  Branches      1466      1450   -16     
=========================================
  Hits          6259      6259           

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[dplewis]

@mtrezza How does this look? Feel free to change the verbiage

[mtrezza]

Does this require any changes, now that #2462 has been merged?

[dplewis]

@mtrezza No changes needed.

[mtrezza]

I believe I have seen some potential for improvement but didn't get around typing it up yet. On my list.