library_bgp_speaker.rst: make an example more complete

also, while i'm here, remove trailing whitespaces in the example.

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>

doc/source/library_bgp_speaker.rst

@@ -20,18 +20,30 @@ instance advertizes some prefixes.
 .. code-block:: python
 
     import eventlet
+
+    # BGPSpeaker needs sockets patched
+    eventlet.patch()
+
+    # initialize a log handler
+    # this is not strictly necessary but useful if you get messages like:
+    #    No handlers could be found for logger "ryu.lib.hub"
+    import logging
+    import sys
+    log = logging.getLogger()
+    log.addHandler(logging.StreamHandler(sys.stderr))
+
     from ryu.services.protocols.bgp.bgpspeaker import BGPSpeaker
-        
+
     def dump_remote_best_path_change(event):
         print 'the best path changed:', event.remote_as, event.prefix,\
             event.nexthop, event.is_withdraw
 
     if __name__ == "__main__":
         speaker = BGPSpeaker(as_number=64512, router_id='10.0.0.1',
                              best_path_change_handler=dump_remote_best_path_change)
-        
+
         speaker.neighbor_add('192.168.177.32', 64513)
-    
+
         count = 1
         while True:
             eventlet.sleep(30)