doc: clarify --no-track option

It is not really about ignoring the config option; it is
about turning off tracking, _even if_ the config option is
set.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-branch.txt

@@ -124,7 +124,8 @@ OPTIONS
 	start-point is either a local or remote branch.
 
 --no-track::
-	Ignore the branch.autosetupmerge configuration variable.
+	Do not set up tracking configuration, even if the
+	branch.autosetupmerge configuration variable is true.
 
 --contains <commit>::
 	Only list branches which contain the specified commit.

Documentation/git-checkout.txt

@@ -90,7 +90,8 @@ guessing results in an empty name, the guessing is aborted.  You can
 explicitly give a name with '-b' in such a case.
 
 --no-track::
-	Ignore the branch.autosetupmerge configuration variable.
+	Do not set up tracking configuration, even if the
+	branch.autosetupmerge configuration variable is true.
 
 -l::
 	Create the new branch's reflog.  This activates recording of