feat: add the ability to constrain memory on service start/clone

Refs dokku/dokku-redis#86

subcommands/create

@@ -21,6 +21,7 @@ service-create-cmd() {
   #F -C|--custom-env "USER=alpha;HOST=beta", semi-colon delimited environment variables to start the service with
   #F -i|--image IMAGE, the image name to start the service with
   #F -I|--image-version IMAGE_VERSION, the image version to start the service with
+  #F -m|--memory MEMORY, container memory limit (default: unlimited)
   #F -p|--password PASSWORD, override the user-level service password
   #F -r|--root-password PASSWORD, override the root-level service password
   declare desc="create a $PLUGIN_SERVICE service"