Add build instructions based on diff from Frank Terbeck.

NOTES

@@ -13,6 +13,16 @@ Since the 1.2 release that tmux depends on libevent. Download it from:
 
 	http://www.monkey.org/~provos/libevent/
 
+To build tmux from a release tarball, do:
+
+	$ ./configure && make
+	$ sudo make install
+
+To build from a version control checkout, the configure script must be
+generated by running:
+
+	$ sh autogen.sh
+
 tmux consists of a server part and multiple clients. The server is created when
 required and runs continuously unless killed by the user. Clients access the
 server through a socket in /tmp. Multiple sessions may be created on a single