important to document : GAMIN dependency

[killerbot]

We have a new dependency (at least on linux) :
- GAMIN package (and server)
- GAMIN devel package

On my boxes : these packages were not installed by default.

[Jenna]

They are dependencies of FileManager-plugin, and the automake-system checks for the existence.
They will also be build-dependencies of debian buildsystem after the next commit.