bootstraping the plugin

I couldn't find In the readme nor the source code a built in way to initialize the plugin. I had to include the ```environments.php``` file in my ```app/Config/bootstrap.php```, but then doing ```CakePlugin::load('Environments')``` was not necessary. 

I added a ```bootstrap.php``` file in the plugin's Config directory, and updated the README to indicate that you should bootstrap the plugin within the ```CakePlugin::load``` or ```CakePlugin::loadAll``` methods.

As a plus, I added working database config in the ```development.php``` environment example, that correctly loads if using the proposed database config file.

Cheers!