Included Gradle instructions

Not sure if this is the best option.
Fix instructions on how to setup AndroidManifest.

On AndroidManifest.xml, android:name must be ContentProvider Class,
not Class implementing DB Contract.
Merge pull request #1 from weltonrodrigo/gradleinstructions

Included Gradle instructions
Merge pull request #2 from weltonrodrigo/manifestfix

Fix instructions on how to setup AndroidManifest.