README is too short

[Steven R. Brandt]

README.md should describe how to compile the code (i.e. what version of scons to use and how to call it)

It should also have examples of how to run the code, i.e. use foo.par to simulate a black plus scalar field… and possibly sample plots of output data.

[Peter Diener]

@Steven R. Brandt Can you check if the current README.md is satisfactory?