docs/develop: introduce intermediate index for each section

The table of content of the top level will include everything that's up
to 2 levels down. Currently this results in a lot of pages and no clear
organization.

Extra index pages allow for more intermediate levels, resulting in less
things being listed in the main page. This way the organization is a bit
clearer, even if this is still not great due to many missing pages and
sections in the documentation currently.

Change-Id: I5bbdd96b3c2ff3334b9ad1b86fd9e7fb00fd63a6
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6008
Tested-by: Commit checker robot <[email protected]>
Reviewed-by: waddlesplash <[email protected]>

docs/develop/file_systems/overview.rst

@@ -1,13 +1,5 @@
-Filesystem drivers
-==================
-
-Filesystem drivers are in src/add-ons/kernel/file_system
-
-A filesystem usually relies on an underlying block device, but that's not
-required. For example, NFS is a network filesystem, so it doesn't need one.
-
-Implementation notes
---------------------
+File systems overview
+---------------------
 
 Each filesystem driver must define a few structures which act as the
 interface between the VFS and the filesystem implementation. These
@@ -89,10 +81,3 @@ Torture and performance tests
 Once the basic operations are working fine, it is a good idea to perform more
 agressive testing. Examples of scripts doing this are available in
 src/tests/add-ons/kernel/file_systems/ for the fat and ext2 filesystems.
-
-.. toctree::
-
-   /file_systems/userlandfs
-   /file_systems/ufs2
-   /file_systems/xfs
-   /file_systems/befs/resources