Updated README.md and contributing.md with more detail

Added some detail to these 2 md files.

Firstly, the assumptions would be good to know, since not everyone is going to necessarily know all the steps, especially if this is their first project to contribute to on github.

Secondly, I had trouble using git@github.com:SpaceAdvocates/penny4nasa in my recursive git clone, but the problems were corrected once I switched to https://github.com/SpaceAdvocates/penny4nasa

Thirdly, I added details on creating the local-config.php file. This is something that I was not familiar with and it took some stumbling to realize what I was missing here.

Further changes may be necessary to add links, but these seemed good for now.