docs: Move project contribution info to sep file

[crandmck]

Changes in this pull request

Similar to contentauth/c2pa-ios#86, moves project contribution info out of the main README.

Also made some other small edits, e.g. changing headings to sentence case to match docs convention.

Types of changes

Docs only.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.78%. Comparing base (e62ba32) to head (307e830).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main      #60   +/-   ##
=========================================
  Coverage     65.78%   65.78%           
  Complexity        9        9           
=========================================
  Files            56       56           
  Lines          1920     1920           
  Branches        218      218           
=========================================
  Hits           1263     1263           
  Misses          510      510           
  Partials        147      147           

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[redaranj]

Thanks for splitting this out @crandmck - looks good. I see a few content areas in the README that I need to expand on - will do that in my own documentation PR once we clear the code PRs.