[ci skip] Update docs with Action Cable Redis dependency

Action Cable's test `test/subscription_adapter/redis_test.rb` fail if
Redis is not installed and running.

Following the guides `development_dependen there's no mention to this.

guides/source/development_dependencies_install.md

@@ -288,3 +288,46 @@ NOTE: Using the rake task to create the test databases ensures they have the cor
 NOTE: You'll see the following warning (or localized warning) during activating HStore extension in PostgreSQL 9.1.x or earlier: "WARNING: => is deprecated as an operator".
 
 If you're using another database, check the file `activerecord/test/config.yml` or `activerecord/test/config.example.yml` for default connection information. You can edit `activerecord/test/config.yml` to provide different credentials on your machine if you must, but obviously you should not push any such changes back to Rails.
+
+### Action Cable Setup
+
+Action Cable uses Redis as its default subscriptions adapter ([read more](action_cable_overview.html#broadcasting)). Thus, in order to have Action Cable's tests passing you need to install and have Redis running.
+
+#### Install Redis From Source
+
+Redis' documentation discourage installations with package managers as those are usually outdated. Installing from source and bringing the server up is straight forward and well documented on [Redis' documentation](http://redis.io/download#installation).
+
+#### Install Redis From Package Manager
+
+On OS X, you can run:
+
+```bash
+$ brew install redis
+```
+
+Follow the instructions given by Homebrew to start these.
+
+In Ubuntu just run:
+
+```bash
+$ sudo apt-get install redis-server
+```
+
+On Fedora or CentOS (requires EPEL enabled), just run:
+
+```bash
+$ sudo yum install redis
+```
+
+If you are running Arch Linux just run:
+
+```bash
+$ sudo pacman -S redis
+$ sudo systemctl start redis
+```
+
+FreeBSD users will have to run the following:
+
+```bash
+# portmaster databases/redis
+```