Add readme

README.md

+# Redis store with CAS for ActiveSupport
+
+__`redis-activesupport-with-cas`__ provides a cache for __ActiveSupport__ including 'Compare and Swap' methods.
+ 
+It is based on [redis-store](https://github.com/redis-store/redis-store) and may used with [Identity Cache](https://github.com/Shopify/identity_cache).
+
+## Installation
+
+```ruby
+# Gemfile
+gem 'redis-activesupport-with-cas'
+```
+
+## Usage
+
+```ruby
+ActiveSupport::Cache.lookup_store :redis_store_with_cas # { ... optional configuration ... }
+```
+
+## Running tests
+
+```shell
+gem install bundler
+git clone https://git.alwin-it.de/ruby-redis/redis-activesupport-with-cas.git
+cd redis-activesupport-with-cas
+bundle install
+bundle exec rake
+```
+
+## Copyright
+
+2017 Rajko Albrecht, released under the MIT license
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