Link to virtualplants.github.io in the doc

[baugetfa]

In the README of openalea.rtfd.io there are links to the Link to virtualplants web site, specifically to the git workflow documentation.

Do we need to keep these links or do we migrate the git workflow documentation to the new documentation website ?

I think we should decrease the number of web interface.

[pradal]

Sure. We need to migrate it, bcause we have to maintain it.