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.
The simplest way is to use an the ebuild and install via portage (emerge). This takes care of dependencies, creating the couchdb user, basically everything you need to get up and running.
sudo emerge -av couchdb # will ask you before it actually installs