Add contributing ref to Agile Guidelines

[andrew-m-leonard]

Description of change

Add link to https://github.com/adoptium/adoptium/wiki/Adoptium-Agile-Guidelines in Contributing page

Checklist

• npm test passes
• documentation is changed or added (if applicable)
• permission has been obtained to add new logo (if applicable)
• contribution guidelines followed here

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.47%. Comparing base (48fec4e) to head (9382a21).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3060   +/-   ##
=======================================
  Coverage   99.47%   99.47%           
=======================================
  Files          90       90           
  Lines        4968     4968           
  Branches      624      624           
=======================================
  Hits         4942     4942           
  Misses         26       26           

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[steelhead31]

Looks good.