Demo of typical changes to experiment template when making a specific experiment

[sandypreiss]

Not planning to merge. This draft PR exists to demonstrate the typical changes that we make to the experiment template branch when making a new branch for a specific experiment.

• Make a new branch with the exp_ prefix. Depending on the experiment, this could branch off the experiment template branch or a prior specific experiment branch if that's easier. For example, if we make a bunch of changes for the exp-complex-experiment branch, and then want to run a second batch for that experiment with a few small tweaks, it makes more sense to branch exp-complex-experiment-batch-2 from exp-complex-experiment.
• Change the S3 bucket name in run_iteration.sh and summarize.py
• Change prepare.py to create the scenarios you need for this experiment. This is typically the most complex and thought-intensive step in defining a new experiment. All the other steps are just logistics; this is where we have to think through how to define the scenarios for the experiment.
• Update the README to reflect these changes.

Then follow the steps in the README to run the experiment.