allow concurrency to be used in development mode

man/foreman.1.ronn

@@ -25,6 +25,10 @@ application type.
 
 The following options control how the application is run:
 
+  * `-c`, `--concurrency`:
+    Specify the number of each process type to run. The value passed in
+    should be in the format `process=num,process=num`
+
   * `-s`, `--screen`:
     Run the application as a series of screen windows rather than interleaved
     in stdout.