Apply suggestions from code review of branch jpeg-capture-in-stacking

Co-authored-by: Beth Probert <beth_probert@outlook.com>

src/openflexure_microscope_server/things/camera/__init__.py

@@ -31,6 +31,8 @@ class JPEGBlob(Blob):
 
 
 class PNGBlob(Blob):
+    """A class representing a PNG image as a LabThings FastAPI Blob"""
+
     media_type: str = "image/png"