librem5-flash-image: Add test for default script name

scripts/librem5-flash-image

@@ -264,6 +264,8 @@ def get_board(path):
 
     In case of doubt return the default board.
 
+    >>> get_board("/a/b/librem5-flash-image")
+    'librem5r4'
     >>> get_board("/a/b/librem5-devkit-flash-image")
     'devkit'
     >>> get_board("/a/b/librem5r2-flash-image")