Docs: Self Check docs additions

I'm going through the process of setting up EG self check stations for our migrations, and I have a few things I would like to add to the self check documentation. If anyone else has any suggestion for things that were not covered but should have been when they implemented self check, please add them to the list.

 1. Document how to auto logon, it is simple, adding username= and password= to URL, but it should be included.

 2. Add some suggestions for kiosk browsers.

 3. Add a note about the barcode pattern regex YAOUS needing to be set for barcodes to be recognized.

 4. Add info about where to edit the self check receipts.

 5. Add info about where the template and css files are for those that want to customize the self check interface.

 6. Add some screenshots of the interface.

 7. Add a description of all the functions that can be performed in the self check.

I'll have my work in progress at the following github gist.
https://gist.github.com/stompro/7811c59905a321807518