Update plugins.md

docs/plugins.md

@@ -158,6 +158,16 @@ A exec plugin is any executable that accepts a
 single argument on its command line - the name of
 a YAML file containing its configuration.
 
+> TODO: more restrictions on plugin to allow one exec
+> to be both a _g_ and a _t_ plugin.
+> - first arg could be `generate` or `transform`,
+>   (the name of the configuration file move to be
+>   the 2nd arg), or
+> - by default an exec plugin behaves as a tranformer
+>   (with one arg, the config file name)
+>   unless a flag `-g` is provided, switching the
+>   exec plugin to behave as a generator.
+
 A generator plugin accepts nothing on `stdin`, but emits
 generated resources to `stdout`.
 
@@ -222,7 +232,6 @@ go build -buildmode plugin -tags=plugin \
     $dir/${kind}.go
 ```
 
-
 #### Caveats
 
 Go plugins allow kustomize extensions that