Readme improvements

[klieret]

Brainstorming:

• Add an authors section, also good place to place sponsors/supporters and write about workshops that have already happenend

• List of notebooks: How about having a very short description after each item. Intro to markdown: Markdown is an easy way to format documents that is very popular in the programming community

• Copying files locally: Nice that you explain how to paste in the termnal, but I think this is a tiny bit confusing (people will do Ctrl-Shift-C in their browser? In fact they don't need to copy in the terminal for now anyway)

• Add HEP/CMS callout in a second paragraph at the top: "In particular we will analyze data from the CMS experiment, that ..."

[stale]

This issue or pull request has been automatically marked as stale because it has not had recent activity. Please manually close it, if it is no longer relevant, or ask for help or support to help getting it unstuck. Let me bring this to the attention of @klieret @wdconinc @michmx for now.