Deno plugin section in the manual

[yos1p]

Suggestions for the Manual. One of Deno interesting feature is that developers can create a Rust plugin that we can call through our Deno code. Maybe we can put this in another section?

Here's some idea that we can include in the documentation: ( Ref: https://nodejs.org/dist/latest-v15.x/docs/api/addons.html )

• How plugin can interact with the Deno runtime / app
• Simple "hello world" example of plugin