Add the add command to help

libexec/jenv-help

@@ -143,7 +143,7 @@ if [ -z "$1" ] || [ "$1" == "jenv" ]; then
   [ -z "$usage" ] || exit
   echo
   echo "Some useful jenv commands are:"
-  print_summaries commands local global shell install uninstall rehash version versions which whence
+  print_summaries commands local global shell install uninstall rehash version versions which whence add
   echo
   echo "See \`jenv help <command>' for information on a specific command."
   echo "For full documentation, see: https://github.com/hikage/jenv#readme"