Rework description

[tintou]

The current description is:

VGrive is a client (back-end and front-end) for Google Drive made in Vala. Automatically detects changes in local and remote files and syncs them.

It might be worth reworking the description to cover some points:

• Do not start the description with the application name, we already have the name written above in all contexts.
• Do not mention the language it is written into: Vala is so nice, but the end-user probably won't care that much.

You might emphasis to the fact that it is simple to setup and allows some integration with the system.