additional /cmd application directory clarification

README.md

@@ -14,7 +14,7 @@ Main applications for this project.
 
 The directory name for each application should match the name of the executable you want to have (e.g., `/cmd/myapp`).
 
-Don't put a lot of code in the application directory.  If you think the code can be imported and used in other projects, then it should live in the `/pkg` directory.
+Don't put a lot of code in the application directory.  If you think the code can be imported and used in other projects, then it should live in the `/pkg` directory. If the code is not reusable or if you don't want others to reuse it, put that code in the `/internal` directory. You'll be surprised what others will do, so be explicit about your intentions!
 
 It's common to have a small main function that imports and invokes the code from the `/internal` and `/pkg` directories.