Merge branch 'update_apptainer' into 'master'

Update Apptainer documentation

See merge request !387

content/applications/user_software/using_apptainer.md

@@ -55,6 +55,12 @@ and indicate you would like to use Apptainer.
 
 ## Use images on HCC resources
 
+{{% notice info %}}
+Apptainer can not be used on the login node. To run Apptainer on HCC resources, please start an [interactive session]({{< relref "../../../../submitting_jobs/creating_an_interactive_job.md" >}}) 
+or submit [SLURM job]({{< relref "../../submitting_jobs/" >}}). Next, please make sure the `apptainer` module is loaded such that the Apptainer variables are correctly set.
+If Apptainer is run on the login node, or the `apptainer` module is not loaded, various error messages can occur.
+{{% /notice %}}
+
 To use Apptainer on HCC machines, first load the `apptainer `module.
 Apptainer provides a few different ways to access the container.
 Most common is to use the `exec` command to run a specific command