Design doc and streamlined onboarding on environment setup for Colab

[jmogarrio]

There's some additional work on #41 that might be helpful to fully understand the tradeoffs here. Initial design doc at go/ddf-runtimes, though I expect that doc to need substantial revamping following the streamlining I did this morning.

• [x] #41
• [x] Update go/ddf-runtimes.
• [x] Follow up on #89

[jmogarrio]

I've updated go/ddf-runtimes, though mostly stripped a lot of the details that dealt with problems we were experiencing at the time of writing. I also added a lot of the specific runtime details that I investigated while prototyping. I'm not up to date on the current development direction, and I suspect having a more detailed description of runtime details should likely be incorporated into the final documentation.

Assigning this to Ben so he can check out the document and figure out if it needs additional work.

[benwulfe]

This work is covered by https://github.com/tnc-br/ddf-isoscapes/issues/131