Update video_chatcompletions_example_restapi.ipynb

[jfilcik]

update comments to describe the new code.

Description

Checklist "# Sample 10 frames from the video file using pymovie library",

• [x] I have read the contribution guidelines
• [x] I have coordinated with the docs team (mldocs@microsoft.com) if this PR deletes files or changes any file names or file extensions.
• [x] This notebook or file is added to the CODEOWNERS file, pointing to the author or the author's team.

[jfilcik]

@steeler18 can you review?