chore: Create a proper site documentation for Maven Spoon Plugin

[surli]

We should be able to generate a standard Maven Plugin Site documentation for Spoon Maven Plugin, especially as we start to have a lot of different options now.
(see: http://maven.apache.org/guides/development/guide-plugin-documentation.html)

This site should be deployed and included in Spoon documentation.

[monperrus]

I would propose that the README.md of Spoon Maven Plugin is the unique and central page for documentation: https://github.com/SpoonLabs/spoon-maven-plugin

And this README is already quite good.

OK to close?

[surli]

And this README is already quite good.

it already miss quite a few explanation about the available mojo options for advanced users. I don't think it would be good to put them in the README since it would be very long, but I don't think we should leave them undocumented.
Maybe adding a Github wiki would be enough there.