git clone git://git.colivre.coop.br/noosfero.git
or if you are in a network managed by fascists, you can use
git clone http://git.colivre.coop.br/repos/noosfero.git
(this is slower, and worse in several aspects)
HACKING and INSTALL. Alternatively, you can read the instructions on-line directly from the source code repository.