add pre-commit hooks for convenient formatting checks (#4387)

* add pre-commit hooks

* ignore yamls in packaging/*

* add pre-commit to contributing guide lines

* Update CONTRIBUTING.md
Co-authored-by: Nicolas Hug <contact@nicolas-hug.com>

* remove some hooks

* fix docstrings

* fix end of files
Co-authored-by: Nicolas Hug <contact@nicolas-hug.com>

test/test_video_reader.py

@@ -112,8 +112,8 @@ DecoderResult = collections.namedtuple(
     "DecoderResult", "vframes vframe_pts vtimebase aframes aframe_pts atimebase"
 )
 
-"""av_seek_frame is imprecise so seek to a timestamp earlier by a margin
-The unit of margin is second"""
+# av_seek_frame is imprecise so seek to a timestamp earlier by a margin
+# The unit of margin is second
 seek_frame_margin = 0.25