Added explicit creation of non-root

Added explicit creation of non-root to the dockerfile. In some situations (e.g., containerd on Kubernetes) the home directory for the user (/home/nonroot) isn't necessarily created when the image is loaded. In this case, things get tricky because the nonroot user doesn't seem to have write access to any other paths. Also, explicitly coding in the useradd seems to be best practice (though this is obviously less relevant).

Docker/Dockerfile

@@ -221,6 +221,7 @@ RUN cd /fastsurfer ; python3 FastSurferCNN/download_checkpoints.py --all && \
 
 # Set FastSurfer workdir and entrypoint
 #  the script entrypoint ensures that our conda env is active
+RUN useradd -m -s /bin/bash -u 1000 -g 1000 nonroot
 USER nonroot
 WORKDIR "/fastsurfer"
 ENTRYPOINT ["/fastsurfer/Docker/entrypoint.sh","/fastsurfer/run_fastsurfer.sh"]
@@ -232,4 +233,4 @@ FROM runtime AS runtime_cuda
 
 ENV NVIDIA_VISIBLE_DEVICES=all \
     NVIDIA_DRIVER_CAPABILITIES=compute,utility \
-    NVIDIA_REQUIRE_CUDA="cuda>=8.0"
+    NVIDIA_REQUIRE_CUDA="cuda>=8.0"