add a note about ipfs key in the main helptext

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

core/commands/root.go

@@ -46,6 +46,7 @@ ADVANCED COMMANDS
   pin           Pin objects to local storage
   repo          Manipulate the IPFS repository
   stats         Various operational stats
+  key           Create and manipulate keypairs
 
 NETWORK COMMANDS
   id            Show info about IPFS peers