add note in daemon helptext about new routing type

License: MIT
Signed-off-by: Jeromy <why@ipfs.io>

cmd/ipfs/daemon.go

@@ -121,6 +121,17 @@ environment variable:
 
     export IPFS_PATH=/path/to/ipfsrepo
 
+Routing
+
+IPFS by default will use a DHT for content routing. There is a highly
+experimental alternative that operates the DHT in a 'client only' mode that can
+be enabled by running the daemon as:
+
+    ipfs daemon --routing=dhtclient
+
+This will later be transitioned into a config option once it gets out of the
+'experimental' stage.
+
 DEPRECATION NOTICE
 
 Previously, IPFS used an environment variable as seen below: