Add comments for documentation generation

[akshgpt7]

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.

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.