Document GPUL Schools - overview and organising

[jorgeteixe]

Each event has a overview.md and a organising.md, pretty self explanatory.

For the GPUL Schools we should get the organising done right with as much detail as possible, including: booking the room, generating the images, the meetup, everything.

[jorgeteixe]

Please @gpul-org/schools-maintainers, can any of you pick this up?

[delthia]

I will 🙂