Refine wording of README about delegation to other bodies

This slightly rewords the README to make two points:

• GHC HQ has overall authority over GHC, and delegates that authority to the GHC Steering Committee and the CLC.
• Major language features are expected to go to the GHC Steering Committee.

Decisions about major features and the language that GHC compiles fall in the remit of the GHC Steering Committee.

Hmm. What is a "major feature" other than "the language that GHC compiles? I'm not sure what you have in mind here.

As to the "overall authority" bit, I suppose that's fair enough. But I don't want to get into a debate about who "wins" if theres is a conflict betwene the (small, by-invitation) GHC HQ group, and the (larger, call-for-nonimations) groups like the GHC SC or CLC. (Answer "everyone loses".) If there is any anxiety here, I'm content to leave it a bit ambiguous.

Hmm. What is a "major feature" other than "the language that GHC compiles? I'm not sure what you have in mind here.

The ghc-proposals readme has a few examples, although I agree it is a bit ambiguous when a feature needs to go through the proposals process. And there has been a drift towards the steering committee primarily overseeing language changes and not necessarily other features.

As to the "overall authority" bit, I suppose that's fair enough. But I don't want to get into a debate about who "wins" if theres is a conflict betwene the (small, by-invitation) GHC HQ group, and the (larger, call-for-nonimations) groups like the GHC SC or CLC. (Answer "everyone loses".) If there is any anxiety here, I'm content to leave it a bit ambiguous.

I'm hopeful this isn't actually that controversial a point, but I can understand if you'd rather leave it untried!