Add module level docstrings.

src/openflexure_microscope_server/things/smart_scan.py

@@ -1,3 +1,12 @@
+"""The core sample scanning functionality for the OpenFlexure Microscope.
+
+SmartScan provides sample scanning functionality including automatic background
+dectection (via the `BackgroundDetectThing`) and automatic path planning via
+`scan_planners`. It manages the directories of past scans via `scan_directories`.
+It also controls external processes for live stitching composite images, and
+the creation of the final stitched images.
+"""
+
 from typing import Optional, Mapping
 import threading
 import os