Some Documentation/Usage Notes

Note to $self -- here are some tidbits ToDo:

o   --help  doesn't work on:
        git-hash-object
	git-init-db
	git-write-tree

o   There is an odd <any-file-on-the-filesystem> argment named
    in the git-hash-object documentation.  Would <file> be better
    and more consistent?  Or is there some subtlety that I am missing?

o   Someone might want to check my --template=<dir> description
    on git-init-db, or make it clearer.

o   Work towards moving uniform description of all environment
    variables in one includable/referenceable Documentation/ file?