docs: Explain PipeWire role, add graphics

doc/dox/media/SoundStack.svg

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doc/dox/overview-for-users.md

@@ -24,7 +24,7 @@ they just use the PulseAudio API provided by PipeWire. Therefore, PulseAudio too
 
 ## PipeWire overview
 
-Normally, a system with PipeWire also runs WirePlumber.
+Normally, a system with PipeWire also runs **WirePlumber.**
 
 **PipeWire** only *provides* the functionality for transporting and transforming audio and video. It is *used* by a session manager.
 
@@ -60,7 +60,7 @@ Some specific properties:
 
 Relationships between different object types (`type` property):
 
-![Object type relationship](pipewire-object-types-relationship.drawio.png)
+![Object type relationship](pipewire-object-types-relationship.drawio.svg)
 
 ```mermaid
 flowchart LR

doc/dox/overview.dox

@@ -1,5 +1,38 @@
 /** \page page_overview Overview
 
+# The role of PipeWire
+
+Today’s Linux systems use ALSA (Advanced Linux Sound Architecture) to play and record sound and video.
+ALSA is built directly into the Linux Kernel including drivers for sound cards, and applications can use ALSA to play sound.
+However, each sound card can only be used by one application at a time – which is one reason why another layer like PipeWire is required:
+It mixes multiple audio streams together and sends that to ALSA directly.
+
+\image html SoundMixing.drawio.svg
+
+There are a number of popular sound servers for Linux like JACK for low latency or PulseAudio.
+PipeWire is the newest one, combining the advantages of its predecessors.
+
+Applications are programmed to support a certain backend, or sometimes they support more than one.
+PipeWire provides API interfaces that look like e.g. ALSA or PulseAudio, so an application only supporting PulseAudio actually works with PipeWire because it looks like PulseAudio to the application.
+Therefore, tools like `pavucontrol` *also* work for PipeWire!
+
+\image html LinuxSoundStack.drawio.svg
+
+# What do I need?
+
+Normally, a system with PipeWire also runs **WirePlumber.**
+
+While **PipeWire** *provides* the functionality for transporting and transforming audio and video, it does not actively react to events like connecting Bluetooth earbuds.
+This is the task of the session manager which *uses* PipeWire.
+
+There is one PipeWire *server* which is used by a number of PipeWire *clients* (the processes that produce/consume multimedia).
+PipeWire, as well as WirePlumber, run in *userspace,* so interfacing with them with `systemd` (and `journald` etc.)
+happens in *user context* with the `--user` flag, for example
+`systemctl --user status pipewire.service` or `journalctl --user -fu wireplumber.service`.
+
+**WirePlumber** provides [Session Management](https://pipewire.pages.freedesktop.org/wireplumber/design/understanding_session_management.html): It enables new devices when they appear on ALSA, creates and configures nodes,
+create links between nodes to route sound from an application to a consumer, etc.
+
 # Concepts
 
 ## The PipeWire Server