Add proper return code for i3-msg

man/i3-msg.man

@@ -90,6 +90,15 @@ See the -m option for continuous monitoring.
 i3-msg is a sample implementation for a client using the unix socket IPC
 interface to i3.
 
+=== Exit status:
+
+0:
+if OK,
+1:
+if invalid syntax or unable to connect to ipc-socket
+2:
+if i3 returned an error processing your command(s)
+
 == EXAMPLES
 
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