Link to 0.10.3 tag instead of master branch

It may be less confusing for new users if the docs link them to the current stable release. It could reduce issues like [this one](#1988)

Author: berfarah

README.md

@@ -84,8 +84,14 @@ If you'd like to chat, we have a [community slack](http://amserializers.herokuap
 Thanks!
 
 ## Documentation
+
+If you're reading this at https://github.com/rails-api/active_model_serializers you are
+reading documentation for our `master`, which may include features that have not
+been released yet. Please see below for the documentation relevant to you.
+
 - [0.10 (master) Documentation](https://github.com/rails-api/active_model_serializers/tree/master)
-  - [![API Docs](http://img.shields.io/badge/yard-docs-blue.svg)](http://www.rubydoc.info/gems/active_model_serializers/0.10.2)
+- [0.10.3 (latest release) Documentation](https://github.com/rails-api/active_model_serializers/tree/v0.10.3)
+  - [![API Docs](http://img.shields.io/badge/yard-docs-blue.svg)](http://www.rubydoc.info/gems/active_model_serializers/0.10.3)
   - [Guides](docs)
 - [0.9 (0-9-stable) Documentation](https://github.com/rails-api/active_model_serializers/tree/0-9-stable)
   - [![API Docs](http://img.shields.io/badge/yard-docs-blue.svg)](http://www.rubydoc.info/github/rails-api/active_model_serializers/0-9-stable)