timeline: add week20.txt

Now we are getting started for real :)

timeline/week20.txt

+Week 19 (11.05.-17.05.)
+=======================
+
+[ ] design of importer	(11.05.)
+
+	- What components are required?
+
+	- What language/stack to use? Here we need to keep
+	  available libraries in mind.
+
+	- sketch out APIs between components
+
+[ ] build up prototype  (11.05.+)