New Post: Update the location of Build.ps1 in ReadMe.txt

The ReadMe.txt in SCSM PowerShell Cmdlets BETA 4 stated that the "Build.ps1" is in the current directory (which by default is C:\Program Files\Common Files\SMLets). However, the actual location of "Build.ps1" should be under the "C:\Program Files\Common Files\SMLets\Src" sub-directory instead.