more help text for partitioning

There are a lot of users that use Ubuntu as first Linux distribution.

Partitioning is always the more delicate operation, especially for dual-boot, but also because most new users have confused ideas about it.

So, I'd like to have, during partitioning operations, both in live and alternate installation method, a guide to partitioning. In alternate, it can be positioned when it's asked for the partition metod (automatic or manual).

In this guide, there will be an introduction of partitions in Linux, for example, what's /, what's /home and what's swap, and so on: how external disk are mounted etc etc.

In this way, new user can have more clear ideas when he must to partion the disk (especially in manual mode). I think that this guide during installation can be very helpful.