doc: Add notes about -mon option mode=control argument.

The mode=control argument configures a QMP monitor.

Signed-off-by: Ali Shirvani <alishir@routerhosting.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <0799f0de89ad2482672b5d61d0de61e6eba782da.1621407918.git.alishir@routerhosting.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

qemu-options.hx

@@ -3799,8 +3799,11 @@ DEF("mon", HAS_ARG, QEMU_OPTION_mon, \
     "-mon [chardev=]name[,mode=readline|control][,pretty[=on|off]]\n", QEMU_ARCH_ALL)
 SRST
 ``-mon [chardev=]name[,mode=readline|control][,pretty[=on|off]]``
-    Setup monitor on chardev name. ``pretty`` is only valid when
-    ``mode=control``, turning on JSON pretty printing to ease
+    Setup monitor on chardev name. ``mode=control`` configures 
+    a QMP monitor (a JSON RPC-style protocol) and it is not the
+    same as HMP, the human monitor that has a "(qemu)" prompt.
+    ``pretty`` is only valid when ``mode=control``, 
+    turning on JSON pretty printing to ease
     human reading and debugging.
 ERST