docs: update tagline and add support statement

[isc-tleavitt]

Internal ref: APPS-24342

Also adds standard CONTRIBUTING.md

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 25.16%. Comparing base (d27c893) to head (7e05fc8).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #555   +/-   ##
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  Coverage   25.16%   25.16%           
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  Files          18       18           
  Lines        2647     2647           
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  Hits          666      666           
  Misses       1981     1981           

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[isc-tleavitt]

@isc-rsingh would love your take on this too given your concerns that @isc-bspead raised

[isc-rsingh]

Sounds good as a way to communicate that the solution is embedded within the InterSystems product. Server-side source control is one of the source control methodologies this extension supports, but it provides more than that.