Add main reason for faking data...

README.fakedata.md

@@ -3,7 +3,8 @@ swiftmpifakestepsim
 ===================
 
 The swiftmpifakestepsim program works much like swiftmpistepsim, except that
-it generates fake logs:
+it generates fake sizes messages and can be scaled to run on any number of MPI
+ranks.
 
 ```
 Usage: ./swiftmpifakestepsim [options] nr_messages logfile.dat