Update deb dockerfile and entrypoint like PR shenxn#69 from upstream

Author: olivervhansen

deb/Dockerfile

@@ -12,4 +12,11 @@ COPY gpgparams install.sh entrypoint.sh VERSION /protonmail/
 # Install dependencies and protonmail bridge
 RUN bash install.sh
 
+# Add a user 'protonmail' with UID 8535
+RUN useradd -u 8535 -d /home/protonmail protonmail \
+    && mkdir -p /home/protonmail \
+    && chown protonmail: /home/protonmail
+# change to non-privileged user for extra security
+USER protonmail
+
 ENTRYPOINT ["bash", "/protonmail/entrypoint.sh"]

deb/entrypoint.sh

@@ -2,6 +2,10 @@
 
 set -ex
 
+# Go to current user's homedir
+cd
+echo "Running as user '$USER' (UID '$UID') in '$PWD'"
+
 # Initialize
 if [[ $1 == init ]]; then