Refactor README.md: Update example command for running Python app

README.md

@@ -1,5 +1,3 @@
-# crpropa_singularity
-
 # CRPropa Apptainer Image
 
 This repository contains a recipe to build an [Apptainer](https://apptainer.org/user-guide/introduction.html) image for [CRPropa](https://github.com/CRPropa/CRPropa3) - the Cosmic Ray Propagation Framework.
@@ -8,24 +6,19 @@ This repository contains a recipe to build an [Apptainer](https://apptainer.org/
 
 A prebuilt container is available in the "releases" section.
 
-To run your Python script (`app.py`) using CRPropa, use the following command:
-
-```bash
-./Apptainer.sif python3 app.py
-```
-
-Example output:
+To run our example Python app (`example.py`), use the following command:
 
 ```bash
-Python version
-3.6.8 (default, Nov  9 2021, 14:44:26) 
-[GCC 8.5.0 20210514 (Red Hat 8.5.0-3)]
-we can import crpropa, cool.
+apptainer exec crpropa.sif python ./example.py
+CosmicRay at z = 0
+  source:  Particle 1000010010, E = 200 EeV, x = 100 0 0 Mpc, p = -1 0 0
+  current: Particle 1000010010, E = 0.998292 EeV, x = -13173.3 0 0 Mpc, p = -1 0 0
+Propagated distance 13273.263588242868 Mpc
 ```
 
-## Creating the Container
+## Advanced: Creating the Container
 
-### Production: Create SIF File
+### Create SIF File
 
 To build the SIF file for production, run:
 
@@ -47,6 +40,6 @@ apptainer build --fakeroot --sandbox sandbox ./crpropa.def
 
 Follow the [installation guide](https://apptainer.org/docs/admin/main/installation.html) for Apptainer, which works well on recent Ubuntu versions (24.04).
 
-### Additional Notes
+## Additional Notes
 
-The container is based on the Rocky Linux 9 Docker image.
+The container is currently based on the Rocky Linux 9 Docker image.