Update readme

[almanilsson]

Better description, should probably remove the very unprofessional jokes

[magnuspalmblad]

What jokes? Apparently I missed something. But a good README file is always a good idea, since this is usually the first people read.

[almanilsson]

@magnuspalmblad oh just the usage comment that has been left since the beginning "Open cytoscape, open your code editor and press any key to play (it has to be ctrl-R)."

[almanilsson]

Readme should probably link to docs: https://workflomics.readthedocs.io/en/pumetric/basics/pubmetric.html