Web folder path fixes

Hi Scott,

Since I've already made those minor fixes that we've discussed here: https://github.com/roots/bedrock/pull/32#issuecomment-33139582, I thought you might concider adding them to your web-folder branch.

* Add absolute path to ```autoload.php``` and ```application.php``` files in ```wp-config.php```
* Add ```/web``` path to the Custom Content Directory and to the absolute path to the WordPress directory
* Update README.md