Respond to help command by showing usage info

bin/gvm

@@ -34,9 +34,7 @@ else
 	if [ -f "$GVM_ROOT/scripts/$command" ]; then
 		shift
 		"$GVM_ROOT/scripts/$command" "$@"
-	elif [[ -n $command ]]; then
-		display_fatal "Unrecognized command line argument: '$command'"
-	else
+	elif [[ -z $command || $command = help ]]; then
 		echo "Usage: gvm [command]
 
 Description:
@@ -47,6 +45,7 @@ Commands:
   get        - gets the latest code (for debugging)
   use        - select a go version to use
   diff       - view changes to Go root
+  help       - display this usage text
   implode    - completely remove gvm
   install    - install go versions
   uninstall  - uninstall go versions
@@ -58,5 +57,7 @@ Commands:
   pkgset     - manage go packages sets
   pkgenv     - edit the environment for a package set
 "
+	else
+		display_fatal "Unrecognized command line argument: '$command'"
 	fi
 fi