According to included README: "Run "./autogen.sh" to generate the configure scripts if nessesary. The man page "doc/rtorrent.1" must be generated with "docbook2man rtorrent.1.xml" if it is missing.
This comes up fairly often. The man page is horribly outdated and not particularly useful. See bug 921745, bug 957320, bug 1012100.
*** This bug has been marked as a duplicate of bug 1012100 ***