docs/interop: Delete qmp-intro.txt

qmp-intro.txt is quite small and provides very little information
that isn't already in the documentation elsewhere.  Fold the example
command lines into qemu-options.hx, and delete the now-unneeded plain
text document.

While we're touching the qemu-options.hx documentation text,
wordsmith it a little bit and improve the rST formatting.

Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20230515162245.3964307-4-peter.maydell@linaro.org>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

qemu-options.hx

@@ -4170,26 +4170,42 @@ DEF("qmp", HAS_ARG, QEMU_OPTION_qmp, \
     QEMU_ARCH_ALL)
 SRST
 ``-qmp dev``
-    Like -monitor but opens in 'control' mode.
+    Like ``-monitor`` but opens in 'control' mode. For example, to make
+    QMP available on localhost port 4444::
+
+        -qmp tcp:localhost:4444,server=on,wait=off
+
+    Not all options are configurable via this syntax; for maximum
+    flexibility use the ``-mon`` option and an accompanying ``-chardev``.
+
 ERST
 DEF("qmp-pretty", HAS_ARG, QEMU_OPTION_qmp_pretty, \
     "-qmp-pretty dev like -qmp but uses pretty JSON formatting\n",
     QEMU_ARCH_ALL)
 SRST
 ``-qmp-pretty dev``
-    Like -qmp but uses pretty JSON formatting.
+    Like ``-qmp`` but uses pretty JSON formatting.
 ERST
 
 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. ``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``, 
+    Set up a monitor connected to the chardev ``name``.
+    QEMU supports two monitors: the Human Monitor Protocol
+    (HMP; for human interaction), and the QEMU Monitor Protocol
+    (QMP; a JSON RPC-style protocol).
+    The default is HMP; ``mode=control`` selects QMP instead.
+    ``pretty`` is only valid when ``mode=control``,
     turning on JSON pretty printing to ease
     human reading and debugging.
+
+    For example::
+
+      -chardev socket,id=mon1,host=localhost,port=4444,server=on,wait=off \
+      -mon chardev=mon1,mode=control,pretty=on
+
+    enables the QMP monitor on localhost port 4444 with pretty-printing.
 ERST
 
 DEF("debugcon", HAS_ARG, QEMU_OPTION_debugcon, \