Update README to elaborate the usage and tips for Prerelease Test feature.
Update README to elaborate the usage and tips for Prerelease Test feature.

ubi-agni/industrial_ci,geoffreychiou/industrial_ci,geoffreychiou/industrial_ci,ros-industrial/industrial_ci,ubi-agni/industrial_ci,ros-industrial/industrial_ci,ros-industrial/industrial_ci,tecnalia-advancedmanufacturing-robotics/industrial_ci,tecnalia-advancedmanufacturing-robotics/industrial_ci,tecnalia-advancedmanufacturing-robotics/industrial_ci