Add additional info to Semaphore section of README
Add additional info to Semaphore section of README

To configure Semaphore, Branch History URL should always be used, not
Branches URL

[Finishes #39252577]

genebygene/projectmonitor,BuildingSync/projectmonitor,pivotal/projectmonitor,genebygene/projectmonitor,dgodd/projectmonitor,mabounassif/projectmonitor-docker,dgodd/projectmonitor,pivotal/projectmonitor,BuildingSync/projectmonitor,remind101/projectmonitor,dgodd/projectmonitor,genebygene/projectmonitor,pivotal/projectmonitor,remind101/projectmonitor,BuildingSync/projectmonitor,pivotal/projectmonitor,BuildingSync/projectmonitor,mabounassif/projectmonitor-docker,mabounassif/projectmonitor-docker,remind101/projectmonitor,dgodd/projectmonitor,remind101/projectmonitor,mabounassif/projectmonitor-docker,genebygene/projectmonitor