add ascii block diagram to howto

doc/howto.md

@@ -2,6 +2,29 @@
 
 This is the step-by-step documentation how to use muxsa.  For an overview on muxsa please watch the [Demonstration video (a.k.a. the making of Network Security 2020)](https://nks-devel3.rus.uni-stuttgart.de/muxsa/making_of_netsec_2020.mp4) and keep the [muxsa block diagram](muxsa-blockdiagram.png) in mind.
 
+
+    muxsa block diagram
+
+    +-------------+    +-------------+    +-------------+    +-------------+
+    | slides.pptx | -> | Powerpoint  | -> | muxsa-      | -> | 0000.png,   |
+    |             |    | win in KVM  |    | kvm2png     |    | 0001.png, ..|
+    +_____/~~~~~~~+    +-------------+    +-------------+    +_____/~~~~~~~+
+                                                                |
+                                             +------------------+
+                                             V
+                       +-------------+    +-------------+    +-------------+
+                +----> | audio.m4a   | -> | muxsa-      | -> | film.mp4    |
+                |      |             |    | pngaac2mp4  |    |             |
+                |      +_____/~~~~~~~+    +-------------+    +_____/~~~~~~~+
+                |                           ^
+                |                           +------------------+
+                |                                              |
+    +-------------+    +-------------+    +-------------+    +-------------+
+    | Audacity    | -> | LabelTrack  | -> | muxsa-al2fc | -> |slides.concat|
+    |             |    |             |    |             |    |             |
+    +-------------+    +_____/~~~~~~~+    +-------------+    +_____/~~~~~~~+
+
+
 The author uses muxsa with Debian GNU/Linux 12 ("bookworm").  The muxsa scripts
 and the other software packages used are not very specific to this Linux
 distribution, so muxsa should work with other distros as well. However, some