New feature for ReadmeAnyFromPod - specify the file to use as content source

I'm writing a command-line app and want the contents of the README to come from the POD in the actual script file - not the 'main module' of the dist. So I added that functionality to ReadmeAnyFromPod.

Its default behavior is unchanged, but if in your dist.ini you specify the the path to a file for the option 'from_filename', it will use the POD in the specified file instead of the POD in the main module.

[ReadmeAnyFromPod / MarkdownInRoot]
from_filename = bin/foo