Add a README.md file to the enabler project.

enabler/README.md

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+Public Transport Enabler
+========================
+
+This is a Java library allowing you to get data from public transport providers.
+Look into [NetworkProvider.java](https://github.com/schildbach/public-transport-enabler/blob/master/enabler/src/de/schildbach/pte/NetworkProvider.java) for an overview of the API.
+
+Using providers that require secrets
+------------------------------------
+
+For some providers a secret like an API key is required to use their API.
+Copy the `secrets.properties.template` file to `secrets.properties` like so:
+
+    $ cp test/de/schildbach/pte/live/secrets.properties.template test/de/schildbach/pte/live/secrets.properties
+
+You need to request the secrets directly from the provider. For Navitia based providers, you can [request a secret here](http://www.navitia.io/register).
+
+How to run live tests?
+----------------------
+
+Make sure the test you want to run does not require a secret and if it does, see above for how to get one.
+Once you have the secret or if your provider does not need one, you can run the tests in your IDE.
+Both IntelliJ and Eclipse have excellent support for JUnit tests.
+
+If you prefer to run tests from the command line, you can comment out the test exclude at the end of
+[build.gradle](https://github.com/schildbach/public-transport-enabler/blob/master/enabler/build.gradle#L30)
+and use this command to only execute a test for a single provider:
+
+    $ gradle -Dtest.single=ParisProviderLive test
+
+This uses the `ParisProvider` as an example.
+Just replace it with the provider you want to test.