Update README with additional information and instructions.

place_tracker/README.md

@@ -1,10 +1,70 @@
 # Place Tracker
 
 A sample place tracking app that uses the [google_maps_flutter](https://github.com/flutter/plugins/tree/master/packages/google_maps_flutter) plugin. 
+Keep track of your favorite places, places you've visited, and places you want to go. View details
+about these places, show them on a map, and get directions to them.
+
+**This sample is not currently in a finished state. We're in the process
+of building it out. This sample currently only works on Android (see Caveat below).**
+
+## Goals
+
+* Learn how to create an interface composed of GoogleMap and other widgets.
+* Learn how to show, control, and modify a GoogleMap widget.
+* Learn how to place a marker on a map.
+
+## The important bits
+
+### `place_map.dart`
+
+This page shows a full-screen GoogleMap widget with place markers. Provides examples of how
+to stack other widgets on top of a GoogleMap widget, how to add markers to a map, and how to make
+other flutter widgets interact with the GoogleMap widget.
+
+### `place_details.dart`
+
+This page shows a detailed view of a single place. Provides examples of how to place a
+GoogleMap widget inside of a ListView and how to disable certain touch gestures on the map.
 
 ## Getting Started
 
-For help setting up the plugin, see the plugin's [README](https://github.com/flutter/plugins/tree/master/packages/google_maps_flutter) page.
+To run this sample app, you will need an API key.
+
+Get an API key at <https://cloud.google.com/maps-platform/>.
+
+Specify your API key in the application manifest `android/app/src/main/AndroidManifest.xml`:
+
+```xml
+<manifest ...
+  <application ...
+    <meta-data android:name="com.google.android.geo.API_KEY"
+               android:value="YOUR KEY HERE"/>
+```
+
+For additional help setting up the plugin, see the plugin's [README](https://github.com/flutter/plugins/tree/master/packages/google_maps_flutter) page.
 
 For help getting started with Flutter, view our online
 [documentation](https://flutter.io/).
+
+## Caveat
+
+The google_maps_flutter plugin provides an *unpublished preview* of the Flutter API for Google Maps:
+* Dart APIs for controlling and interacting with a GoogleMap view from Flutter
+  code are still being consolidated and expanded. The intention is to grow
+  current coverage into a complete offering. Issues and pull requests aimed to
+  help us prioritize and speed up this effort are very welcome.
+* Currently the plugin only supports Android as it embeds a platform view in the
+  Flutter hierarchy which is currently only supported for Android ([tracking
+  issue](https://github.com/flutter/flutter/issues/19030)).
+
+## Questions/issues
+
+If you have a general question about any of the techniques you see in
+the sample, the best places to go are:
+
+* [The FlutterDev Google Group](https://groups.google.com/forum/#!forum/flutter-dev)
+* [The Flutter Gitter channel](https://gitter.im/flutter/flutter)
+* [StackOverflow](https://stackoverflow.com/questions/tagged/flutter)
+
+If you run into an issue with the sample itself, please file an issue
+in the [main Flutter repo](https://github.com/flutter/flutter/issues).