util/util_readme: Update post_util.md for MyST Parser

This file is appended to Documentation/util.md by the util_readme.sh
script, and contains toctree entries for utilities with more in-depth
documentation than the description automatically pulled from the
description.md files throughout the util directory. As of commit
35599f9a6671 (Docs: Replace Recommonmark with MyST Parser), the syntax
for creating a toctree has changed, so update this post_util.md
accordingly.

Change-Id: Ia7ae3c513781e53512763578fd97db7e2f75e65c
Signed-off-by: Nicholas Chin <nic.c3.14@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82163
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
diff --git a/util/util_readme/post_util.md b/util/util_readme/post_util.md
index 892dc8a..b0b7bac 100644
--- a/util/util_readme/post_util.md
+++ b/util/util_readme/post_util.md
@@ -1,10 +1,14 @@
 ## In depth documentation
 
-* [abuild](util/abuild/index.md)
-* [cbfstool](util/cbfstool/index.md)
-* [ifdtool](util/ifdtool/index.md)
-* [intelp2m](util/intelp2m/index.md)
-* [smmstoretool](util/smmstoretool/index.md)
+```{toctree}
+:maxdepth: 1
+
+abuild <util/abuild/index.md>
+cbfstool <util/cbfstool/index.md>
+ifdtool <util/ifdtool/index.md>
+intelp2m <util/intelp2m/index.md>
+smmstoretool <util/smmstoretool/index.md>
+```
 
 ## Generated documentation