timeline: add week21.txt

doc/timeline/week21.txt

+Week 21 (18.05. - 24.05.)
+=======================
+
+[~] containerize prototype
+
+-> for development, I'll be using docker-compose for now
+
+-> want to have anything in one setup so it is easy to develop on and
+   demonstrate
+
+[ ] build example application on dataset
+
+-> what should it even do?
+
+-> what should it be written in?
+
+-> how should it be deployed?