The official documentation has moved to http://docs.couchdb.org — The transition is not 100% complete, but http://docs.couchdb.org should be seen as having the latest info. In some cases, the wiki still has some more or older info on certain topics inside CouchDB.
You can check out the code using the svn command:
svn co http://svn.apache.org/repos/asf/couchdb/trunk couchdb
Committers should use the secure repository:
svn co https://svn.apache.org/repos/asf/couchdb/trunk couchdb
Read more about version control at the Apache Software Foundation.
Read the README file for install instructions: CouchDB README