Update book cover and reference page on the ISC website

[spier]

After #44 is live, we could also update the following two assets to correctly describe who is driving this book

• the book cover (I have the files for this somewhere)
• the referring page on the isc website.

[jeffabailey]

#44 is live, @rrrutledge or @spier do you know the next step?

[jeffabailey]

@spier do you know the next steps?

[spier]

@jeffabailey I do :)

the referring page on the isc website.

You can edit this file here as you see fit, and send a PR to get the updated info about the book live on https://innersourcecommons.org/

the book cover (I have the files for this somewhere)

Still true that I have to find the files somewhere. I think I created this with gimp.

In the easiest case might replace the names of the previous authors (Daniel Izquierdo & José Manrique López) with "ISPO Working Group". What do you think?