Update build instructions for Android for versions >= 6
Merge pull request #100 from darktears/update-crosswalk-6

Update build instructions for Android for versions >= 6
Add 'deploy on android' section in documentation.

This section tries to describe how to deploy apks packaged with Crosswalk
to app store for both IA and ARM architectures.

BUG=https://crosswalk-project.org/jira/browse/XWALK-1240