Update readme (#1525)
Update readme (#1525)

* update the README:

* drop Rx1 support
* drop global apollo-codegen documentation (it is still in the code but
ther is no need to advertise it anymore)
* add documentation about coroutines support
* add documentation about espresso support

* formating

* Keep npm codegen for now

* Second parameter should be the apolloClient

* better

apollostack/apollo-android,apollostack/apollo-android,apollographql/apollo-android,apollographql/apollo-android,apollographql/apollo-android,apollostack/apollo-android