More pre-reading

Floor Drees writes, "I found the following links quite helpful as
pre-reading material (for the weekend 😊)".

Add them to the event site, with some tweaks:
- separating articles from books
- linking books to some publicly available reviews

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Change-Id: Ife0d2163a594a1ae3fda9d7ebcb9ec1d313afed5