update media repository implementation docs

docs/media_repository.rst

@@ -12,9 +12,14 @@ Each item of media is assigned a ``media_id`` when it is uploaded.
 The ``media_id`` is a randomly chosen, URL safe 24 character string.
 Metadata such as the MIME type, upload time and length are stored in the
 sqlite3 database indexed by ``media_id``.
-Content is stored on the filesystem under a "content" directory. Thumbnails are
-stored under a "thumbnails" directory.
+Content is stored on the filesystem under a ``"local_content"`` directory.
+Thumbnails are stored under a ``"local_thumbnails"`` directory.
 The item with ``media_id`` ``"aabbccccccccdddddddddddd"`` is stored under
-``"local/content/aa/bb/ccccccccdddddddddddd"``. Its thumbnail with width
+``"local_content/aa/bb/ccccccccdddddddddddd"``. Its thumbnail with width
 ``128`` and height ``96`` and type ``"image/jpeg"`` is stored under
-``"local/thumbnails/aa/bb/ccccccccdddddddddddd/128-96-image-jpeg"``
+``"local_thumbnails/aa/bb/ccccccccdddddddddddd/128-96-image-jpeg"``
+Remote content is cached under ``"remote_content"`` directory. Each item of
+remote content is assigned a local "``filesystem_id``" to ensure that the
+directory structure ``"remote_content/server_name/aa/bb/ccccccccdddddddddddd"``
+is appropriate. Thumbnails for remote content are stored under
+``"remote_thumbnails/server_name/..."``