PC-NONE: Explain migration cleanup process

[jdgage]

Description

Add comment explaining the issue we found and our process to clean up.

Checklist

• I have made any necessary updates to the documentation
• I have checked there are no unnecessary IDE warnings in this PR
• I have checked there are no unintentional line ending changes
• I have added tests where applicable
• If I have made any changes to the code, I have used the IDE auto-formatter on it
• If I have made any changes to website flow, I have updated the Flow Miro Board
• If I have made any changes to website flow, I have checked forward and back behaviour is still consistent
• If I have made any changes to content strings or resource files, I have followed the documentation

Screenshots

n/a