Onionoo is a web-based protocol to learn about currently running Tor relays and bridges. Onionoo itself was not designed as a service for human beings---at least not directly. Onionoo provides the data for other applications and websites which in turn present Tor network status information to humans.
Onionoo users should head over to https://onionoo.torproject.org/ to
learn more about using Onionoo.
Onionoo service operators should read INSTALL.
Onionoo contributors should start reading CONTRIB.md and, once it's
available, run ant doc and read the generated JavaDocs.