allow installation of man and html doc from the man and html branches
This patch introduces a make target "quick-install-html" which installs
the html documentation from the branch origin/html, without the need for
asciidoc/xmlto. This is analogous to the existing "quick-install-doc"
target for the man pages.
We advertise these targets in the INSTALL file now.
Signed-off-by: Michael J Gruber <michaeljgruber+gmane@fastmail.fm> Signed-off-by: Junio C Hamano <gitster@pobox.com>