Add help with translations

Add info with how to help with the translations in the start page of the
application and in the readme.md of the project.

README.md

@@ -77,6 +77,12 @@ If no platform is provided, all the platforms will be done in sequence.
 
 You can also use multiple platforms e.g. `gulp <taskname> --osx64 --linux64`.
 
+## Languages
+
+Betaflight Configurator has been translated to several languages. The application will be shown in your system language if a translation into this language is available. You can help [translating the application into your language](http://betaflight.oneskyapp.com).
+
+If you prefer to have the application in english, you can execute the program from the command line with the parameter `--lang=en` or you can create a script or a shortcut with this parameter included.
+
 ## Notes
 
 ### WebGL

_locales/en/messages.json

@@ -292,7 +292,7 @@
         "message": "Contributing"
     },
     "defaultContributingText": {
-        "message": "If you would like to help make Betaflight even better you can help in many ways, including:<br /><ul><li>Answering other users questions on the forums and IRC.</li><li>Contributing code to the firmware and configurator - new features, fixes, improvements</li><li>Testing <a href=\"https://github.com/Betaflight/betaflight/pulls\" target=\"_blank\">new features/fixes</a> and providing feedback.</li><li>Helping out with <a href=\"https://github.com/betaflight/betaflight/issues\" target=\"_blank\">issues and commenting on feature requests</a>.</li><li></li></ul>"
+        "message": "If you would like to help make Betaflight even better you can help in many ways, including:<br /><ul><li>Answering other users questions on the forums and IRC.</li><li>Contributing code to the firmware and configurator - new features, fixes, improvements</li><li>Testing <a href=\"https://github.com/Betaflight/betaflight/pulls\" target=\"_blank\">new features/fixes</a> and providing feedback.</li><li>Helping out with <a href=\"https://github.com/betaflight/betaflight/issues\" target=\"_blank\">issues and commenting on feature requests</a>.</li><li>Collaborate by <a href=\"http://betaflight.oneskyapp.com\" target=\"_blank\">translating the configurator application</a> into your language.</li><li></li></ul>"
     },
     "defaultChangelogHead": {
         "message": "Configurator - Changelog"