Companion piece to blog post: https://medium.com/@murki/chaining-multiple-sources-with-rxjava-20eb6850e5d9
This code example uses the Flickr API which requires you to use your own API Key, which you can get here: https://www.flickr.com/services/api/misc.api_keys.html
Once you get the key, you can add it to your local gradle.properties file as FLICKR_API_KEY="xxxxxxxxxxxxxxxxxx" because it will be retrieved by gradle at build time via https://github.com/murki/chaining-rxjava/blob/master/app/build.gradle#L23
