Doc how to export on windows.

Windows paths in interactive mode are an issue. Use command line
directly or some other way of specing paths without using \ character.

Author: rouilj

doc/admin_guide.txt

@@ -294,7 +294,10 @@ Migrating Backends
 
 1. Stop the existing tracker web and email frontends (preventing changes).
 2. Use the roundup-admin tool "export" command to export the contents of
-   your tracker to disk.
+   your tracker to disk. (If you are running on windows see
+   `issue1441336 <https://issues.roundup-tracker.org/issue1441336>`_
+   on how to use the command line rather than interactive mode to
+   exprt data.)
 3. Copy the tracker home to a new directory.
 4. Delete the "db" directory from the new directory.
 5. Set the value of the ``backend`` key under the ``[database]``