Fix lessons as nose is 4 and not 0 now

Fix incompatibility with OTP23. Fix #9

Also fix README to refer to latest rebar version compatible with OTP21
Also add CI for RaspberryPi OS versions and pynab 0.9.1

Fix correction of exercise 5 (fixes #6)

Merge pull request #7 from mehdichaouch/patch-1

Update README.md