README update

Signed-off-by: Markus Birth <markus@birth-online.de>

README.md

@@ -18,3 +18,13 @@ Preparations
    (If you're using [uv](https://docs.astral.sh/uv/), it'll do this automatically on the
    first run.)
 
+
+Usage
+-----
+
+Just run the `porta_dump.py` directly - you might have to set the execute bits first:
+
+    chmod a+x porta_dump.py
+    ./porta_dump.py
+
+It'll write all files into the current directory.