README: Qualify "current core team" with a date

[andreasabel]

haskell-admins/README.md

Lines 34 to 39 in a429411

	The current core team is:
	* Gershom Bazerman (co-lead) (@gershomb)
	* Davean Scies (co-lead) (@davean)
	* Herbert Valerio Riedel (@hvr)
	* Rick Elrod (@relrod)

This information could be correct but feels a bit improbable.

Could the information be qualified with a date, like "since" for each member and "last updated" for the whole information?