Add android note (#3631)

* add android note

* move to sub bullet

Author: jbolinger

README.md

@@ -219,7 +219,11 @@ threading restrictions.
 
 Thus, the following are not supported:
 
-- Android
+- Android 
+  - Consider [Firebase](https://firebase.google.com), which includes many of these APIs.
+  - It is possible to use these libraries in many cases, although it is unsupported.
+    You can find examples, such as [this one](https://github.com/GoogleCloudPlatform/android-docs-samples/tree/master/speech/SpeechRecognitionClient),
+    in this [example repository](https://github.com/GoogleCloudPlatform/android-docs-samples) but consider the risks carefully before using these libraries in an application.
 - Alpine Linux (due to netty-tcnative requiring glibc, which is not present on Alpine)
 - Raspberry Pi (since it runs on the ARM architecture)
 - Google App Engine Standard Java 7