README: remove usage instructions, and refer to the help topic instead. The diff for the change can be somewhat hard to read, but all it does is replace the `Basic Use' and `Support for svn:externals' sections with the following section: Further Reading --------------- More information on how to use hgsubversion is available from within Mercurial in the `subversion` help topic. To view it, use:: $ hg help subversion The Restructured Text source for this topic is also available in the file ``hgsubverson/help/subversion.rst``.