Add import.paths key to config.yaml.

Used to tell Dougal which parts of the filesystem may be
accessed by users via the API (more specifically, via the
`/files/` API endpoints).

etc/config.yaml

@@ -39,6 +39,18 @@ imports:
     mounts:
         - /srv/mnt/Data
 
+    # These paths can be exposed to end users via the API. They should
+    # contain the locations were project data, or any other user data
+    # that needs to be accessible by Dougal, is located.
+    #
+    # This key can be either a string or an object:
+    # - If a string, it points to the root path for Dougal-accessible data.
+    # - If an object, there is an implicit root and the first-level
+    #   paths are denoted by the keys, with the values being their
+    #   respective physical paths.
+    # Non-absolute paths are relative to $DOUGAL_ROOT.
+    paths: /srv/mnt/Data
+
 queues:
     asaqc:
         request: