Document branch.autosetupmerge.
Document branch.autosetupmerge.

This patch documents the branch.autosetupmerge config option, added
by commit 0746d19a.

Signed-off-by: Paolo Bonzini  <67a772724e2fbc123894e2d469547b8302dd9fd5@gnu.org>
Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git