Fix broken link to community contributing guide

[jack-berg]

Build is currently broken after open-telemetry/community#2051 moved the community contributor guide.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.19%. Comparing base (6fc1d21) to head (f9578d7).
Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6616      +/-   ##
============================================
- Coverage     90.30%   90.19%   -0.11%     
- Complexity     6260     6281      +21     
============================================
  Files           690      697       +7     
  Lines         18762    18903     +141     
  Branches       1853     1852       -1     
============================================
+ Hits          16943    17050     +107     
- Misses         1258     1281      +23     
- Partials        561      572      +11     

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