Link to or include dev training course content

[mattyg]

There is great content in these courses that is buried and difficult to discover. If we don't want to maintain it all ourselves, at least link to it so it is discoverable.

Video course: https://resources.holochain.org/self-paced-training-signup/?__s=6juhqkpqogg41j5vc6fs&utm_source=drip&utm_medium=email&utm_campaign=Master+Holochain+at+Your+Own+Pace

Slides & excercises: https://github.com/holochain-immersive