Add logger

I am adding a small text about the logger and the planetary movie.

data/cs.md

@@ -43,3 +43,18 @@ SWIFT uses the parallel-hdf5 library to read and write snapshots
 efficiently on distributed file systems. Through careful tuning of
 Lustre parameters, SWIFT can write snapshots at the maximal disk
 writing speed of a given system.
+
+
+### Logger
+
+In SWIFT, we developed a new way of writing the information contained in 
+snapshots (Hausammann and Gonnet (in prep.)).
+In cosmological  simulations, the time scale of the different particles
+can differ by a few order of magnitudes.
+This technique reduces the data entropy by writing the particles according
+to their own time scale.
+SWIFT is able this way to increase the time resolution of the output while
+keeping the files to a decent size.
+
+<div class="videowrapper"><iframe width="100%" height="100%" src="https://www.youtube.com/embed/6aBry0CUgVw" frameborder="0" allowfullscreen></iframe>
+</div>