Introduction points to almost empty page "Hardware Reference"

We know the hardware of the Devkit so the first link Hardware Reference on

https://developer.puri.sm/Librem5/Introduction.html

Should point to an appropriate page. This also relates to #18.

Having things like RAM, CPU Module, modem, wifi would be start we could then fill in more details via MRs. The page should provide two separate sections for the devkit and the phone.