[PATCH] doc: config, tell readers of `git help --config`

[Philip Oakley <philipoakley@iee.email>]

The `git help` command gained the ability to list config variables in
3ac68a93fd (help: add --config to list all available config, 2018-05-26)
but failed to tell readers of the config documenation itself.

Provide that cross reference.

Signed-off-by: Philip Oakley <philipoakley@iee.email>
---
I noticed this omission while reviewing Ævar Arnfjörð Bjarmason's
[PATCH v2 2/5] help: correct usage & behavior of "git help --guides"
<patch-v2-2.5-039639a0dd3-20210910T112545Z-avarab@gmail.com>.

My initial comment is in <2493437c-01c5-ddcc-6a61-666f87e70f20@iee.email>
and follow up, that is was out of scope to Ævar's series, in
<8c72d383-4ae2-b96c-6886-7c36153d8991@iee.email>.

This patch is independednt of the ab/help-config-vars series.
---
 Documentation/git-config.txt | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Documentation/git-config.txt b/Documentation/git-config.txt
index 2dc4bae6da..992225f612 100644
--- a/Documentation/git-config.txt
+++ b/Documentation/git-config.txt
@@ -71,6 +71,9 @@ codes are:
 
 On success, the command returns the exit code 0.
 
+A list of all available configuration variables can be obtained using the
+`git help --config` command.
+
 [[OPTIONS]]
 OPTIONS
 -------
-- 
2.33.0.windows.2