Attract more users

[svenvanderburg]

Let's try to attract more users in general and specifically beta pilot testers.

### Tasks
- [ ] https://github.com/carpentries-incubator/lesson-gpu-programming/issues/107
- [ ] https://github.com/carpentries-incubator/lesson-gpu-programming/issues/108
- [ ] https://github.com/carpentries-incubator/lesson-gpu-programming/issues/109
- [ ] https://github.com/carpentries-incubator/lesson-gpu-programming/issues/110
- [ ] https://github.com/carpentries-incubator/lesson-gpu-programming/issues/111
- [ ] https://github.com/carpentries-incubator/lesson-gpu-programming/issues/112

[svenvanderburg]

@isazi these are the most important things we can do to make this lesson more visible. How do you feel about it? I could also pick up some tasks if you want.