Add widgets to list of client features

[HarHarLinks]

matrix.org/CONTENT.md

Lines 164 to 173 in f758eca

	[extra.features]
	e2ee = false
	spaces = false
	voip_1to1 = false
	voip_jitsi = false
	threads = false
	sso = false
	oauth = false
	multi_account = false
	multi_language = false

As of #3449 we have an explicit list of "Experimental" non-spec features for clients.

Widgets are one such feature that is implemented by multiple clients.

Related: #3230