QMP: Update README file

A number of changes I prefer to do in one shot:

- Fix example
- Small clarifications
- Add multiple monitors example
- Add 'Development Process' section
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>
(cherry picked from commit d29f3196)

QMP/README

@@ -7,60 +7,85 @@ Introduction
 The QEMU Monitor Protocol (QMP) allows applications to communicate with
 QEMU's Monitor.
 
-QMP is JSON[1] based and has the following features:
+QMP is JSON[1] based and currently has the following features:
 
 - Lightweight, text-based, easy to parse data format
-- Asynchronous events support 
-- Stability
+- Asynchronous messages support (ie. events)
+- Capabilities Negotiation
 
-For more information, please, refer to the following files:
+For detailed information on QMP's usage, please, refer to the following files:
 
 o qmp-spec.txt      QEMU Monitor Protocol current specification
-o qmp-commands.txt  QMP supported commands
+o qmp-commands.txt  QMP supported commands (auto-generated at build-time)
 o qmp-events.txt    List of available asynchronous events
 
 There are also two simple Python scripts available:
 
-o qmp-shell       A shell
-o vm-info         Show some information about the Virtual Machine
+o qmp-shell  A shell
+o vm-info    Show some information about the Virtual Machine
+
+IMPORTANT: It's strongly recommended to read the 'Stability Considerations'
+section in the qmp-commands.txt file before making any serious use of QMP.
+
 
 [1] http://www.json.org
 
 Usage
 -----
 
-To enable QMP, QEMU has to be started in "control mode". There are
-two ways of doing this, the simplest one is using the the '-qmp'
-command-line option.
+To enable QMP, you need a QEMU monitor instance in "control mode". There are
+two ways of doing this.
+
+The simplest one is using the '-qmp' command-line option. The following
+example makes QMP available on localhost port 4444:
 
-For example:
+  $ qemu [...] -qmp tcp:localhost:4444,server
 
-$ qemu [...] -qmp tcp:localhost:4444,server
+However, in order to have more complex combinations, like multiple monitors,
+the '-mon' command-line option should be used along with the '-chardev' one.
+For instance, the following example creates one user monitor on stdio and one
+QMP monitor on localhost port 4444.
 
-Will start QEMU in control mode, waiting for a client TCP connection
-on localhost port 4444.
+   $ qemu [...] -chardev stdio,id=mon0 -mon chardev=mon0,mode=readline \
+                -chardev socket,id=mon1,host=localhost,port=4444,server \
+                -mon chardev=mon1,mode=control
 
-It is also possible to use the '-mon' command-line option to have
-more complex combinations. Please, refer to the QEMU's manpage for
-more information.
+Please, refer to QEMU's manpage for more information.
 
 Simple Testing
 --------------
 
-To manually test QMP one can connect with telnet and issue commands:
+To manually test QMP one can connect with telnet and issue commands by hand:
 
 $ telnet localhost 4444
 Trying 127.0.0.1...
 Connected to localhost.
 Escape character is '^]'.
-{"QMP": {"version": {"qemu": "0.12.50", "package": ""}, "capabilities": []}}
+{"QMP": {"version": {"qemu": {"micro": 50, "minor": 13, "major": 0}, "package": ""}, "capabilities": []}}
 { "execute": "qmp_capabilities" }
 {"return": {}}
 { "execute": "query-version" }
-{"return": {"qemu": "0.12.50", "package": ""}}
+{"return": {"qemu": {"micro": 50, "minor": 13, "major": 0}, "package": ""}}
+
+Development Process
+-------------------
+
+When changing QMP's interface (by adding new commands, events or modifying
+existing ones) it's mandatory to update the relevant documentation, which is
+one (or more) of the files listed in the 'Introduction' section*.
+
+Also, it's strongly recommended to send the documentation patch first, before
+doing any code change. This is so because:
+
+  1. Avoids the code dictating the interface
+
+  2. Review can improve your interface.  Letting that happen before
+     you implement it can save you work.
+
+* The qmp-commands.txt file is generated from the qemu-monitor.hx one, which
+  is the file that should be edited.
 
-Contact
--------
+Homepage
+--------
 
 http://www.linux-kvm.org/page/MonitorProtocol
-Luiz Fernando N. Capitulino <lcapitulino@redhat.com>