README.md: touch-ups by a native English speaker

[ldoolitt]

Grammar, spelling, squelch trailing spaces, and especially change Mhz to MHz

@Dolu1990 I watched your 37c3 talk twice. Looks fantastic!
I'm struggling to understand how all the pieces of NaxRiscv fit together.
Maybe later I can give actual technical contributions, but until then, maybe this simple copy-editing can help.

[Dolu1990]

Thanks :D

[Dolu1990]

I'm struggling to understand how all the pieces of NaxRiscv fit together.Maybe later I can give actual technical contributions,

Hmm if you are interrested, i'm now trying to push https://github.com/SpinalHDL/VexiiRiscv
Being in order, its complexity is more aprochable i would say ? Also, as its framework is one iteration after Nax, so it is generaly cleaner.

Let's me know :)