zeroconf: small fixes in docstring
Use reST role for consistency, import small part of Debian's
proposed_upstream__correct-zeroconf-doc patch from
http://svn.debian.org/viewsvn/python-apps/packages/mercurial/trunk/debian/patches/
% hg debuginstall
Checking encoding (ascii)...
Checking extensions...
Checking templates...
Checking patch...
Checking commit editor...
Checking username...
No problems detected
% hg debuginstall with no username
Checking encoding (ascii)...
Checking extensions...
Checking templates...
Checking patch...
Checking commit editor...
Checking username...
no username supplied (see "hg help config")
(specify a username in your .hgrc file)
1 problems detected, please check your install!