Add alternative entrypoint for better tool runner use

[alxwrd]

Hello!

This adds an alternative entrypoint that matches the package name to allow a simplier way to run via tool runners like uvx.

$ uvx youtube-transcript-api ... --format text
Installed 7 packages in 9ms
An executable named `youtube-transcript-api` is not provided by package `youtube-transcript-api`.
The following executables are available:
- youtube_transcript_api

Use `uvx --from youtube-transcript-api youtube_transcript_api` instead.