Documentation: Fix up toctree

Some files weren't properly hooked up, making Sphinx complain.

Change-Id: If959fa63d4ddbc3916c49c5ad6602e76b12a7e60
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55020
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Reviewed-by: Michael Niewöhner <foss@mniewoehner.de>
Reviewed-by:  Felix Singer <felixsinger@posteo.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

Documentation/infrastructure/index.md

@@ -3,4 +3,4 @@
 This section contains documentation about coreboot infrastructure
 
 ## Jenkins builders and builds
-[Setting up Jenkins build machines](builders.md)
+* [Setting up Jenkins build machines](builders.md)