Add sample transifex status graph

## Example for l10n-canada

 [![Build Status](https://travis-ci.org/OCA/l10n-canada.svg?branch=7.0)](https://travis-ci.org/OCA/l10n-canada)
[![Coverage Status](https://coveralls.io/repos/OCA/l10n-canada/badge.png?branch=7.0)](https://coveralls.io/r/OCA/l10n-canada?branch=7.0)
+[![Transifex Status](https://www.transifex.com/projects/p/l10n-canada/chart/image_png)](https://www.transifex.com/projects/p/l10n-canada)