Add "Author should include JSDoc" to PR template

[yusukebe]

What is the feature you are proposing?

Context: #2615 (comment)

I'm thinking we should improve the PR template to tell every PR that adding a new feature should add TSDoc/JSDoc (if it's necessary) @yusukebe This way we can slowly migrate codebase to use TSDoc/JSDoc

[EdamAme-x]

If this is to be implemented, we also need to add a guide on how to write it (jsdoc).

e.x.
JSDoc must includes description, @ see, @ param, @ returns, if needs @ throws, @ example

[fzn0x]

If this is to be implemented, we also need to add a guide on how to write it (jsdoc).

e.x. JSDoc must includes description, @ see, @ param, @ returns, if needs @ throws, @ example

I have something simpler in mind will create a PR soon :)