Track the number of contributors from repos that use the json-schema topic, over time

Depends on: https://github.com/json-schema-org/ecosystem/issues/1

We define contributors as users who have comitted to the git history.

It should be quite easy to get the current number of contributors using just a few lines.

Getting this historically shouldn't be super difficult, as you can checkout git repos without code (just the log) and do an analysis.

If we expanded the definition of contributions to include Issues and PR reviews, this would probably be different to what most people expect, and getting at historic data would be much more effort, although not impossible.

Would need to do something similar to https://github.com/api7/contributor-graph
There may be an easier approach, but I haven't been able to find one when looking for about half an hour.
(Look at the nice graphs it makes from the data it collects!)

Review the dependency on ecosystem issue #1 and the approaches in the linked community comment, api7/contributor-graph, and git-contributor.com. Start by determining how repositories using the json-schema topic and their git histories will be collected. Done means producing historical contributor counts over time using the stated commit-based definition.