Improve documentation for RelayBandwdith* options

Jesse Adelman noticed that we don't currently describe what
happens very well.

doc/tor.1.txt

@@ -89,14 +89,14 @@ Other options can be specified either on the command-line (--option
     without impacting network performance.
 
 **RelayBandwidthRate** __N__ **bytes**|**KB**|**MB**|**GB**::
-    If defined, a separate token bucket limits the average incoming bandwidth
+    If not 0, a separate token bucket limits the average incoming bandwidth
     usage for \_relayed traffic_ on this node to the specified number of bytes
     per second, and the average outgoing bandwidth usage to that same value.
     Relayed traffic currently is calculated to include answers to directory
     requests, but that may change in future versions. (Default: 0)
 
 **RelayBandwidthBurst** __N__ **bytes**|**KB**|**MB**|**GB**::
-    Limit the maximum token bucket size (also known as the burst) for
+    If not 0, limit the maximum token bucket size (also known as the burst) for
     \_relayed traffic_ to the given number of bytes in each direction.
     (Default: 0)