Provide the full documentation in README.md

[tanius]

Since this is the most visible / most central piece of the Graphryder software stack, this is where most of the documentation should go. It is currently maintained in a wiki on Discourse and we can keep editing it there, but every now and then a version should be copied to README.md. With the exception of the graphryder-api installation instructions, which should go into the README.md over there.