README: document importing components by name/path.

Author: cristianoc

README.md

@@ -169,6 +169,8 @@ external make:
 
 The type of `make` must have a named argument for each prop in the JS component. Optional props have option type. The `make` function will be generated by `genType`.
 
+This assumes that the JS component was exported with a default export. In case of named export, use `@genType.as "componentName"`. To import a nested component, use e.g. `@genType.as "Some.Nested.component"`. 
+
 **NOTE** The argument of `@bs.module`must always be the name of the current file plus `.gen` (In future, this could be automatically generated).
 
 ### Type Expansion and @genType.opaque