Add pre-processing section to README

Added pre-processing instructions to README.

Author: ylked

README.md

@@ -162,6 +162,13 @@ npm run dev
 
 The website is accessible on [http://localhost:5173](http://localhost:5173).
 
+### Pre-processing
+
+```
+pfaedle -x switzerland-260518.osm.pbf -i via/data/gtfs_fp2026_20260311.zip -m rail -c pfaedle/pfaedle.cfg
+python3 via/src/filter.py ./gtfs-out ./via/via-ui/public/data
+```
+
 ## Late policy
 
 - < 24h: 80% of the grade for the milestone