doc: correct example concerning "hg purge" alias in man page "hgrc.5" The "hg purge" alias as currently described in "hgrc.5" only works, if the caller's current working directory is identical to the repository's root directory. This patch slightly modifies the example by adding an empty pattern as a file argument to the "hg status" command, thus forcing this command to list the affected files relative to the current directory.