[PATCH] config doc: add missing list separator for checkout.optimizeNewBranch

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

The documentation added in fa655d8411 ("checkout: optimize "git
checkout -b <new_branch>"", 2018-08-16) didn't add the double-colon
needed for the labeled list separator, as a result the added
documentation all got squashed into one paragraph. Fix that by adding
the list separator.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---

Junio: Feel free to squash this in, but per your recent E-Mail it
doesn't seem you're planning to rewind "next", so this can go on top
of gitster/bp/checkout-new-branch-optim.

 Documentation/config.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index ac71ade256..1546833213 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -1153,7 +1153,7 @@ and by linkgit:git-worktree[1] when 'git worktree add' refers to a
 remote branch. This setting might be used for other checkout-like
 commands or functionality in the future.
 
-checkout.optimizeNewBranch
+checkout.optimizeNewBranch::
 	Optimizes the performance of "git checkout -b <new_branch>" when
 	using sparse-checkout.  When set to true, git will not update the
 	repo based on the current sparse-checkout settings.  This means it
-- 
2.19.0.rc2.392.g5ba43deb5a