doc: config: terminate runaway lists

doc: config: terminate runaway lists

There are many places in git-config(1) where paragraphs that should
logically come after a list are instead appended to the last item of
the list.  This is a well-documented quirk of AsciiDoc, and can be
mitigated by enclosing the list in an open block:

	--
	* first item
	* last item
	--
	+
	New paragraph after the list.

Fix the issue accordingly.

Signed-off-by: Tuomas Ahola <taahol@utu.fi>
Signed-off-by: Junio C Hamano <gitster@pobox.com>