Updated install documentation

[Carles Munyoz]

We have updated the install section of the FWCloud documentation present in the website FWCloud.net.

This update includes information about:

• FWCloud-Websrv service.
• FWCloud-Updater service.
• New structure of services for a typical FWCloud server.
• Migrate from the old directory structure to the new one by means of the FWCloud-Installer script.