Add link to 7.1 release notes in upgrade guide
Add link to 7.1 release notes in upgrade guide

To be consistent with other sections

georgeclaghorn/rails,georgeclaghorn/rails,rails/rails,georgeclaghorn/rails,rails/rails,MSP-Greg/rails,MSP-Greg/rails,georgeclaghorn/rails,MSP-Greg/rails,MSP-Greg/rails,rails/rails,rails/rails