Add documentation on group workspaces

Resolve #426 (closed)

doc.zih.tu-dresden.de/docs/data_lifecycle/workspaces.md

@@ -43,7 +43,8 @@ beegfs
 
 !!! note "Default is `scratch`"
 
-    The default filesystem is `scratch`. If you prefer another filesystem, you have to explictly
+    The default filesystem is `scratch`. If you prefer another filesystem (cf. section
+    [List Available Filesystems](#list-available-filesystems)), you have to explictly
     provide the option `-F <fs>` to the workspace commands.
 
 ### List Current Workspaces