Issue #13: Document new nginx_default_release variable in README.

README.md

@@ -59,6 +59,10 @@ This value determines the largest file upload possible, as uploads are passed th
 
 Set as the `proxy_cache_path` directive in the `nginx.conf` file. By default, this will not be configured (if left as an empty string), but if you wish to use Nginx as a reverse proxy, you can set this to a valid value (e.g. `"/var/cache/nginx keys_zone=cache:32m"`) to use Nginx's cache (further proxy configuration can be done in individual server configurations).
 
+    nginx_default_release: ""
+
+(For Debian/Ubuntu only) Allows you to set a different repository for the installation of Nginx. As an example, if you are running Debian's wheezy release, and want to get a newer version of Nginx, you can install the `wheezy-backports` repository and set that value here, and Ansible will use that as the `-t` option while installing Nginx.
+
 ## Dependencies
 
 None.