kpm pack command line help improvements

[Praburaj]

kpm pack -?

--configuration The configuration to use for deployment
[An Example will be helpful.. There are multiple configurations in a project. Startup[Configuration], Configure[Configuration], Debug/Release etc. It will be nice to have an example]

--no-source Don't include sources of project dependencies
[Something like...Compiles the project as a nuget package and avoid placing C# files]

--runtime Names or paths to KRE files to include
[Suggestion: Example or information on delimiter will be helpful while specifying multiple KREs]

[borgdylan]

C# files -> source files
N.B. (the k runtime runs more than just c#)

[muratg]

@Praburaj , please send your suggestions via a PR.