As the helper script could (and probably always would) be launched from
a directory outside of the source tree, it is convenient to use an absolute path
in Get-Help invocation, just like we do in the `build.ps1` invocation below.
Also, quoting might be necessary for paths with spaces.
When using build.ps1 as a developer, we may be working in a shell that
does not have the ability to run the PowerShell script due to signing.
Add a little helper that launches the script properly to not require the
user to disable code signature on scripts.