Fix link in workflow.md

Fix broken link - shortcut points to same book.

Author: Amanda Butler

docs/reference/contributing/guidelines/workflow.md

@@ -63,7 +63,7 @@ Pull requests on GitHub have to meet the following requirements to keep the code
 
 #### Release versioning
 
-You can find Mbed OS versioning at [How We Release Arm Mbed OS](how-we-release-arm-mbed-os.html).
+You can find Mbed OS versioning at [How We Release Arm Mbed OS](/docs/v5.8/introduction/how-we-release-arm-mbed-os.html).
 
 ### Pull request categories