docs: fix title levels, remove unneded words

The title applies to the whole page, not just the first section.
And there should be just one title ('# foo') in a given document.

docs/BUILDING_IMAGES.md

@@ -5,7 +5,7 @@ layout: default
 SPDX-License-Identifier: LGPL-2.1-or-later
 ---
 
-# Safely Building Images
+# Building Images Safely
 
 In many scenarios OS installations are shipped as pre-built images, that
 require no further installation process beyond simple `dd`-ing the image to

docs/FILE_DESCRIPTOR_STORE.md

@@ -47,7 +47,7 @@ conveniently be used to serialize service state into and then place in the
 fdstore, in order to implement service restarts with full service state being
 passed over.
 
-# Basic Mechanism
+## Basic Mechanism
 
 The fdstore is enabled per-service via the
 [`FileDescriptorStoreMax=`](https://www.freedesktop.org/software/systemd/man/systemd.service.html#FileDescriptorStoreMax=)
@@ -76,7 +76,7 @@ both operates on IPv4 and IPv6 and treats both more or less the same.).
 
 And that's already the gist of it.
 
-# Seamless Service Restarts
+## Seamless Service Restarts
 
 A system service that provides a client-facing interface that shall be able to
 seamlessly restart can make use of this in a scheme like the following:
@@ -107,7 +107,7 @@ processes remaining skew them), security policies (as processes with possibly
 out-of-date security policies – SElinux, AppArmor, any LSM, seccomp, BPF — in
 effect remain), and similar.
 
-# File Descriptor Store Life-cycle
+## File Descriptor Store Lifecycle
 
 By default any file descriptor stored in the fdstore for which a `POLLHUP` or
 `POLLERR` is seen is automatically closed and removed from the fdstore. This
@@ -148,7 +148,7 @@ way will not receive an automatic `POLLHUP` event anymore if the service code
 issues `close()` on the socket. It must accompany it with an `FDSTOREREMOVE=1`
 notification to the service manager, so that the fd is comprehensively closed.
 
-# Access Control
+## Access Control
 
 Access to the fds in the file descriptor store is generally restricted to the
 service code itself. Pushing fds into or removing fds from the fdstore is
@@ -160,7 +160,7 @@ By default only the main service process hence can push/remove fds, but by
 setting `NotifyAccess=all` this may be relaxed to allow arbitrary service
 child processes to do the same.
 
-# Soft Reboot
+## Soft Reboot
 
 The fdstore is particularly interesting in [soft
 reboot](https://www.freedesktop.org/software/systemd/man/systemd-soft-reboot.service.html)
@@ -181,7 +181,7 @@ continuously).
 For further details see [Resource
 Pass-Through](https://www.freedesktop.org/software/systemd/man/systemd-soft-reboot.service.html#Resource%20Pass-Through).
 
-# initrd Transitions
+## Initrd Transitions
 
 The fdstore may also be used to pass file descriptors for resources from the
 initrd context to the main system. Restarting all processes after the
@@ -198,7 +198,7 @@ The soft reboot cycle transition and the initrd→host transition are
 semantically very similar, hence similar rules apply, and in both cases it is
 recommended to use the fdstore if pinned resources shall be passed over.
 
-# Debugging
+## Debugging
 
 The
 [`systemd-analyze`](https://www.freedesktop.org/software/systemd/man/systemd-analyze.html#systemd-analyze%20fdstore%20%5BUNIT...%5D)

docs/PORTABLE_SERVICES.md

@@ -5,7 +5,7 @@ layout: default
 SPDX-License-Identifier: LGPL-2.1-or-later
 ---
 
-# Portable Services Introduction
+# Portable Services
 
 systemd (since version 239) supports a concept of "Portable Services".
 "Portable Services" are a delivery method for system services that uses