Documentation/git-config: use bulleted list for exit codes

Using a numbered list is confusing because the exit codes are not listed
in order so the numbers at the start of each line do not match the exit
codes described by the following text.  Switch to a bulleted list so
that the only number appearing on each line is the exit code described.

Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-config.txt

@@ -58,13 +58,13 @@ that location (you can say '--local' but that is the default).
 This command will fail with non-zero status upon error.  Some exit
 codes are:
 
-. The config file is invalid (ret=3),
-. can not write to the config file (ret=4),
-. no section or name was provided (ret=2),
-. the section or key is invalid (ret=1),
-. you try to unset an option which does not exist (ret=5),
-. you try to unset/set an option for which multiple lines match (ret=5), or
-. you try to use an invalid regexp (ret=6).
+- The config file is invalid (ret=3),
+- can not write to the config file (ret=4),
+- no section or name was provided (ret=2),
+- the section or key is invalid (ret=1),
+- you try to unset an option which does not exist (ret=5),
+- you try to unset/set an option for which multiple lines match (ret=5), or
+- you try to use an invalid regexp (ret=6).
 
 On success, the command returns the exit code 0.