clean up ppm viewer program

ppm viewer/README.md

@@ -0,0 +1,16 @@
+# PPM image viewer
+
+Reads a ppm image from an input device (AF.dev by default) 
+and displays it on SicTools builtin graphical screen.
+
+To resize and convert your image you can use ffmpeg:
+```{sh}
+ffmpeg -i image.png -vf scale="64x-1" AF.ppm && mv AF.ppm AF.dev
+```
+
+- Source code: ppm.asm
+- Graphical screen: 64x64 at A000
+  - dimensions can be adjusted by changing their values in code
+- Frequency: any
+- Author: Jakob Jesenko, 2026
+