Remove irrelevant sentence from README

[lurch]

IMHO it doesn't make sense now that this repo is in the raspberrypi org rather than the Hexxeh org

[pelwell]

I'm not saying the wording of these paragraphs couldn't be improved (and the spelling - "seperate"), but that sentence justifies the existence of a parallel repo, whether or not it is "official".

[lurch]

But isn't this https://github.com/raspberrypi/rpi-firmware repo precisely what "If the boot firmware files are split off into a seperate repo..." is referring to? 🤷‍♂️
(or perhaps I've simply misunderstood what that sentence is saying, in which case this PR should be closed)

[pelwell]

I read it to mean "if the upstream firmware repo is split then there may be no need for a separate copy", whereas I think you read something along the lines of "if there is an official firmware-binaries-only repo then there is no need for an unofficial one."

Give that we have now between us spent more time pondering this sentence than the rest of humanity combined, I'm going to merge it for the global good.

[pelwell]

Or I would if I had write access.