Add comments for documentation generation

Add comments for all methods of the YouTube class in the `src/youtube-api-deno.ts` file, describing what the method does, and what all parameters it takes.
The information for all methods can be found [here](https://developers.google.com/youtube/v3/docs).

This is so that when the documentation is generated by `deno doc` (https://doc.deno.land/https/raw.githubusercontent.com/akshgpt7/youtube-api-deno/master/src/mod.ts), it's much more explanatory and detailed.