Remove tmux option from man page

Not well supported at this time. See issue #242

man/foreman.1.ronn

@@ -40,10 +40,6 @@ The following options control how the application is run:
     Specify which port to use as the base for this application. Should be
     a multiple of 1000.
 
-  * `-t`, `--tmux`:
-    Runs the processes in a tmux session. Creates one window for each process
-    and an extra window containing the output of each window (requires gawk).
-
 `foreman run` is used to run one-off commands using the same environment
 as your defined processes.