Install Redis

It is common enough on the thoughtbot client projects I've seen this
year to want to install it on machines by default.

README.md

@@ -39,6 +39,7 @@ What it sets up
 * Postgres gem for talking to Postgres from Ruby
 * Qt for headless JavaScript testing via Capybara Webkit
 * Rails gem for writing web applications
+* Redis for storing key-value data
 * Ruby stable for writing general-purpose code
 * RVM for managing versions of the Ruby programming language
 * SSH public key for authenticating with Github and Heroku

mac

@@ -35,6 +35,9 @@ echo "Installing Postgres, a good open source relational database ..."
   successfully brew install postgres --no-python
   successfully initdb /usr/local/var/postgres -E utf8
 
+echo "Installing Redis, a good key-value database ..."
+  successfully brew install redis
+
 echo "Installing ack, for searching the contents of files ..."
   successfully brew install ack