Summary:
Hi, here are some typo fixes in the documentation related to Android native modules:
* Add missing package and imports for the second part of the basic tutorial (register module)
* Add missing `public` keyword
* Remove incongruous word
Closes https://github.com/facebook/react-native/pull/11938
Differential Revision: D4439220
Pulled By: hramos
fbshipit-source-id: e7086fe384ed6238306abf0ee72c944fac53ad7b