[cleanup] See desc

* Remove struct from `embedthumbnail`
* Use bullet lists in readme where numbered list don't make sense
* Fix error introduced in 9c2b75b561 when `ie_result` is `None`

yt_dlp/postprocessor/embedthumbnail.py

@@ -4,7 +4,6 @@ from __future__ import unicode_literals
 import base64
 import imghdr
 import os
-import struct
 import subprocess
 import re