qapi-schema: Document how generated documentation is ordered

Documentation generated with qapi2texi.py is in source order, with
included sub-schemas inserted at the first include directive
(subsequent include directives have no effect).  To get a sane and
stable order, it's best to include each sub-schema just once, or
include it first in qapi-schema.json.  Document that.

While there, drop a few redundant comments.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <1503602048-12268-2-git-send-email-armbru@redhat.com>

qapi-schema.json

@@ -72,22 +72,17 @@
         'q_obj_CpuInfo-base'    # CPU, visible through query-cpu
     ] } }
 
-# QAPI common definitions
-{ 'include': 'qapi/common.json' }
+# Documentation generated with qapi2texi.py is in source order, with
+# included sub-schemas inserted at the first include directive
+# (subsequent include directives have no effect).  To get a sane and
+# stable order, it's best to include each sub-schema just once, or
+# include it first in qapi-schema.json.
 
-# QAPI crypto definitions
+{ 'include': 'qapi/common.json' }
 { 'include': 'qapi/crypto.json' }
-
-# QAPI block definitions
 { 'include': 'qapi/block.json' }
-
-# QAPI event definitions
 { 'include': 'qapi/event.json' }
-
-# Tracing commands
 { 'include': 'qapi/trace.json' }
-
-# QAPI introspection
 { 'include': 'qapi/introspect.json' }
 
 ##