x86_64 is used as a baseline: the "x86_64" entry, whatever status it has,
is transformed into "all", and then the other entries in ARCHITECTURES
either dropped or rearranged appropriately.
Fixed some capitalization and added a paragraph pointing out Medo's
beta status. I think that's important so people don't expect a
polished product, but are amazed at its powerful features at this stage.
