Example usage of 2D pyramid generation from image collection seems incorrect

[liuji1031]

Description

In the example usage provided in the README for generating 2D pyramid from an image collection with a stitching vector, file_pattern is provided instead, which seems inconsistent with the description in the same section.

Files

Please see here and here where Python code differs from the CPP code regarding whether the second argument being a file pattern or a stitching vector file.