Add an RFC about providing an official WSL image

Add an RFC that defines specifications about providing an official WSL Arch Linux image.

This overall topic has already been discussed and mostly hashed out in the related mail thread in the Arch-Dev-Public mailing list.

As a context reminder, this proposal was initially inspired by the related Fedora one and motivated by the fact that a lot of people (like myself) have no other choice than using Windows on their company's workstation (due to internal policy) and for whom WSL is their workaround to access / work with a Linux environment. While there are unofficial WSL images available for Arch Linux, it's fair to say that their overall quality or their development state vary.

See the rendered version.

Signed-off-by: Robin Candau antiz@archlinux.org