Add extra note about enabling internal packages
Add extra note about enabling internal packages

This simply adds an extra note to the 'writing packages' section of the docs which states that you should `meteor add` an internal package to enable it. I ran into this issue and banged my head for a while last night wondering why an internal package was not exposing a template / exported object to the rest of my app. The issue was that I did not `meteor add` it since I assumed that because it was internal source code I did not have to.

Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor