The documentation is written in asciidoc syntax and needs asciidoc installed to be converted into html/manpages. You can create the documentation of perf by typing 'make' in 'tools/perf/Documentation'.
Perf has a git-like interface, so
shows you the basic usage and a list of the most common subcommands and e.g.
perf top help
shows you the help for 'perf top' command