chore: add DEVELOPMENT.md & cleanup README.md

[erisu]

Platforms affected

n/a

Motivation, Context & Description

• Added DEVELOPMENT.md
  • Contains development-specific documentation only.
  • Excluded from the npm package (not intended for release).
• Updated README.md
  • Removed development-related content.
  • Updated requirement section to include a tip to see the official Apache Cordova documentation with links to the appropriate sections.
  • Fixed some badges & layout.

The "Requirements" sections remain high-level. It is expected that developers who develop for the platform or application developers who uses this platform to follow the official Apache Cordova documentation, which provides detailed setup instructions and specifies the supported tool and platform versions.

Testing

n/a

Checklist

• I've run the tests to see all new and existing tests pass
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.39%. Comparing base (347e2ad) to head (c1f7d05).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1883   +/-   ##
=======================================
  Coverage   61.39%   61.39%           
=======================================
  Files          24       24           
  Lines        4919     4919           
=======================================
  Hits         3020     3020           
  Misses       1899     1899           

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