build: add scripts to generate API document into README.md

[Atry]

Description of change

Added npm run watch to continuously build, test and generate API docs. The approach is described at https://stackoverflow.com/questions/56918621/is-it-possible-to-generate-single-page-doc-html-with-typedoc-for-typescript-proj/57052392

Pull-Request Checklist

• Code is up-to-date with the main branch
• npm run lint passes with this change
• npm run test passes with this change
• This pull request links relevant issues as Fixes #0000
• There are new or updated unit tests validating the change
• Documentation has been updated to reflect this change
• The new commits follow conventions outlined in the conventional commit spec

Fixes #26

[codecov]

Codecov Report

Base: 100.00% // Head: 100.00% // No change to project coverage 👍

Coverage data is based on head (d142d54) compared to base (4fe79a6).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #28   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines            1         1           
  Branches         1         1           
=========================================
  Hits             1         1           

Impacted Files	Coverage Δ
src/index.ts	100.00% <ø> (ø)

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