Add exam info

README.md

@@ -103,6 +103,12 @@ through the mailing list.
   the computer rooms in the ETH main building.
   The system language of the computers is English.
   A list of the installed software can be found [here](https://www.ethz.ch/services/en/it-services/catalogue/managed-client/computer-rooms.html).
+    * A virtual machine was created by staff of the Linux Examination Team
+      from the LET. Although it is not exactly the same version as will
+      be used at the exam, it is reasonably close so that you can get an
+      impression. It is avalaible [here](http://idinstallprd.ethz.ch/img/Fedora31s.ova)
+      (User: student, login-password: student) and can be run, e.g., with
+      [VirtualBox](https://www.virtualbox.org/).
 
 * By default, the keyboards will have the Swiss layout.
   There will be a poll for those who want to get a US keyboard instead.