Document strolls

CONTRIBUTING.md

@@ -239,3 +239,15 @@ subtasks, since it's hard to think of a thing that takes multiple
 weeks as one single task -- although sometimes that can happen, for
 example with a single unified change across an entire code base, like
 changing from raw DB queries to using an ORM or something like that.
+
+## Strolls
+
+At OTS, we do "**strolls**".  These are similar to what are called
+"[sprints](https://en.wikipedia.org/wiki/Scrum_sprint)" in Agile/Scrum
+terminology, but at the end of a stroll we feel energized and
+refreshed, not tired and sweaty.
+
+Not all strolls necessarily have the same duration, even within the
+same project.  We choose a stroll's length based on the work to be
+done, how everyone is feeling after immediately preceding strolls, and
+what people's schedules look like during the upcoming stroll.