Add documentation for plugin

[neeftarah]

Hi,

It would be great to introduce, at least, a link to plugins documentations on a plugin's page.

[tomolimo]

Yes, good idea!

[ghost]

It is true that we could offer a link to the related wiki available by the "project wiki" github feature.

Saying that wiki == documentation !

You guys made me think about the readme_url which is declared in a lot of XML files !
And right now, is now reflected in the fronten.

As of now, the link to the readme that was specified in the XML is now displayed.

Example with the processmaker plugins, which @tomolimo created a wiki for, and used the readme_url to link to it !

http://plugins.glpi-project.org/#/plugin/processmaker

Readme_url now displayed ;)