Fix help of debug command

Add help for debug command. It is useful to have it, even if there's no "debug" command (it is 'debug android' or 'debug ios' now).
Update sha of common lib to latest (pointing the merge commit of iOSDebugging PR.

Author: rosen-vladimirov

lib/common

@@ -422,7 +422,22 @@ Options:
         You cannot use --device and --emulator simultaneously.
     --release - If set, produces a release build. Otherwise, produces a debug build.
 --[/]--
-    
+
+--[debug]--
+
+Usage:
+    $ tns debug <Command>
+
+You must run the debug command with a related command.
+
+Debugs your project on a connected device or in a native emulator.
+
+<Command> is a related command that extends the debug command. You can run the following related commands:
+	android - Debugs your project on a connected Android device, native Android emulator or Genymotion emulator.
+	ios - Debugs your project on a connected iOS device or in a native iOS emulator. 
+
+--[/]--
+
 --[debug|android]--
 
 Usage: