Adds clarity for linking work items and issues to PR form

[oZakari]

Overview/Summary

AB#31225
Currently a requirement in PR to link the work items and issues, but not clear where to include them or what keywords to use.

This PR fixes/adds/changes/removes

1. Adds clarity for linking work items and issues to PR form

Breaking Changes

1. None, just text changes to PR form.

As part of this Pull Request I have

• Read the Contribution Guide and ensured this PR is compliant with the guide
• Checked for duplicate Pull Requests
• Associated it with relevant GitHub Issues or ADO Work Items (Internal Only)
• Ensured my code/branch is up-to-date with the latest changes in the main branch
• Ensured PR tests are passing
• Updated relevant and associated documentation (e.g. Contribution Guide, Docs etc.)

[lachaves]

LGTM