Add documentation about running notebooks in Google Colab.

[ileasile]

Now it's not clear (and not tested well yet) how to run Kotlin Notebooks in Google Colab. Document it. Use this notebook as a reference:
#440 (comment)

[ileasile]

@maxandersen Some users in our public Slack complain there is a problem connecting to the runtime (it's connecting infinitely)

Don't you know what could be a reason and how to diagnose it?

[maxandersen]

works for me but let me re-test on fresh notebook.

To debug use Runtime > View runtime logs and look for suspicious log entries.

[maxandersen]

Can confirm that it is not working at the moment - not sure what goes wrong as the runtime log shows the runtime being executed. Something is broken ;/

[maxandersen]

other java jupyter kernels are working for me. weird.