proposed schedule for 6.1 release

[Peter Maydell]

Here's a draft schedule for the 6.1 cycle:

2021-07-13 Soft feature freeze. Only bug fixes after this point.
2021-07-20 Hard feature freeze. Tag rc0
2021-07-27 Tag rc1
2021-08-03 Tag rc2
2021-08-10 Tag rc3
2021-08-17 Release; or tag rc4 if needed
2021-08-24 Release if we needed an rc4

I don't think there's anything much we want to try to avoid
dates-wise, so I just put the target release date in the middle
of August and worked back from there.

Any objections/suggestions ?

thanks
-- PMM