docs: update issue template with contribution details

[sozercan]

Describe the changes in this pull request using active verbs such as Add, Remove, Replace ...

Saw this on https://github.com/deislabs/ratify, thought it was a good idea to encourage contributions

Closes #<issue_ID>

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (013c118) 33.02% compared to head (7d2bd3b) 33.02%.
Report is 2 commits behind head on main.

❗ Current head 7d2bd3b differs from pull request most recent head 940c558. Consider uploading reports for the commit 940c558 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #379   +/-   ##
=======================================
  Coverage   33.02%   33.02%           
=======================================
  Files          17       17           
  Lines        1626     1626           
=======================================
  Hits          537      537           
  Misses       1060     1060           
  Partials       29       29           

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