Restore deleted section of Contributing.md

[stephen-crawford]

Description

I accidentally deleted this section of the Contributing.md section and missed it during review

It originally came from @reta : https://github.com/opensearch-project/OpenSearch/pull/10751/files

Related Issues

Resolves #[Issue number to be closed when this PR is merged]
#12981 (comment)

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Failing checks are inspected and point to the corresponding known issue(s) (See: Troubleshooting Failing Builds)
• Commits are signed per the DCO using --signoff
• Commit changes are listed out in CHANGELOG.md file (See: Changelog)
• Public documentation issue/PR created

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[github-actions]

❕ Gradle check result for 42eeefe: UNSTABLE

• TEST FAILURES:

      1 org.opensearch.remotestore.RemoteStoreStatsIT.testNonZeroPrimaryStatsOnNewlyCreatedIndexWithZeroDocs
      1 org.opensearch.gateway.RecoveryFromGatewayIT.testShardStoreFetchMultiNodeMultiIndexesUsingBatchAction

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.56%. Comparing base (b15cb0c) to head (42eeefe).
Report is 227 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #13415      +/-   ##
============================================
+ Coverage     71.42%   71.56%   +0.14%     
- Complexity    59978    60838     +860     
============================================
  Files          4985     5045      +60     
  Lines        282275   286080    +3805     
  Branches      40946    41432     +486     
============================================
+ Hits         201603   204737    +3134     
- Misses        63999    64439     +440     
- Partials      16673    16904     +231     

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[reta]

@scrawfor99 could you rebase please? some GA actions are failing but should be fixed by #13412, thank you