[Documentation] Create a "Buy preinstalled" for eOS Smartphones

I suggest that we create a " Buy eOS preinstalled smartphones" which would list the companies and web shops that sell eOS smartphone

it could be https://doc.e.foundation/buypreinstalled

We did it for Ubuntu for several years and it really helped people find a local hardware provider https://doc.ubuntu-fr.org/ordinateur_vendu_avec_ubuntu