redesigning the readme

[benvanwerkhoven]

I'd like to give the README a big update at some point, including:

• [x] logo designed by Stijn
• [x] vastly reduce amount of text, just point to documentation
• [ ] more about performance and productivity impact of auto-tuning
• [ ] potential energy gains using auto-tuning with Kernel Tuner
• [x] bunch of logos of institutes where Kernel Tuner is used in production
• [ ] pointers to related tools: Tutorial, Kernel Launcher, Kernel Float, Dashboard
• [ ] listing the Kernel Tuner Developers team as core developers
• [x] categorize the 'please cite these papers' section

Any other suggestions?

[stijnh]

Some suggestions:

• Short list of features at the top (like 4-5 bullets)
• Table showing supported backends
• List of FAQ (could also be in documentation)
• Section on what to do if you run into a bug/issue/feature request.

[stijnh]

This has been resolved by PR #231