Adds a note on the purpose of the blend_export.py script.

tests/blend_export/blend_export.py

@@ -1,4 +1,13 @@
-# blender --background --python .\blend_export.py
+#! blender --background --python .\blend_export.py
+
+"""
+Automates the regeneration of various export formats from golden blend files.
+
+Note: In environments that do not support shebang execution, Blender may be
+invoked from the command line with the arguments from the first line of this
+script.
+"""
+
 import bpy
 import posixpath
 import shutil