Add README to point out the lipstick repository.

Installer-USB-Stick/README

+Since SS14 all files that are part of the LIP-Image are maintained in
+a seperate "lipstick" repository.
+This relocation allows us to clone the repository on the image or
+stick directly. As a result, we can distribute and update the image
+more easily.
+
+The "lipstick" repository can be accessed through redmine [1] (go to
+the "Repository" tab and choose "lipstick" on the right hand side) or
+by cloning the repository [2].
+
+[1]: https://redmine.fsmpi.rwth-aachen.de/projects/lip/repository
+[2]: gitolite@fsmpi.rwth-aachen.de:lipstick