Describe game in README (#84)

A new section has been added to the README that describes the game and
its features.

README.md

@@ -10,9 +10,18 @@
 task is to create a program that can safely manage the airspace above two
 airports.
 
+![screenshot](./docs/static/img/screenshot.png)
+
 The game is designed to provide an open-ended sandbox that players can use to
-freely practice programming. The game provides a language-agnostic gRPC API,
-giving players free choice of programming language or paradigm.
+freely practice programming. It provides a language-agnostic [gRPC] API, giving
+players free choice of programming language or paradigm.
+
+Check out the official [Getting Started](https://auto-traffic-control.com/docs)
+guide to start playing the game.
+
+## Project Status
+
+**Auto Traffic Control** is currently in an early prototyping phase.
 
 ## License
 
@@ -28,3 +37,5 @@ at your option.
 Unless you explicitly state otherwise, any contribution intentionally submitted
 for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
 dual licensed as above, without any additional terms or conditions.
+
+[grpc]: https://grpc.io/