Salt can be easily installed on Gentoo via Portage:
emerge app-admin/salt
Now go to the Configuring Salt page.
Docs for previous releases are available on salt.rtfd.org.
Latest Salt release: 2014.1.13
Try the shiny new release candidate of Salt, v2014.7.0rc6! More info here.
Upcoming SaltStack events, webinars and local meet ups and user groups.