Fix api key instructions

I've updating the instructions to tell people how to generate API keys all by themselves.
Incorporated screen shot sent by Xiao.

Functional testing:
- run "make html"
- in the _build/html directory, run  "python -m SimpleHTTPServer"
- pull up the api.html page and make sure it looks alright.
- click on the image to make sure you can get the full sized version