docs(installing/configure-dns): updated xip example and added alternative method

Corrected information about xip.io and added in alternative method for setting up DNS with AWS ELBs.
This is my bad actually. In translating from the actual domains I used to example domains, I've switched out the subdomain I was using for deis, incorrectly.

I have for example test.akd.onl and *.test.akd.onl, and then I have deis.test.akd.onl and *.deis.test.akd.onl for the apps. I will look through the documentation again, and, considering Matt's comment above, I'll rework this to be accurate.