Fix docker user permissions issues (#1194)

docker-entrypoint.sh

@@ -0,0 +1,10 @@
+#!/usr/bin/env sh
+
+# If we are root, ensure the files in /out are writable
+# by the dce user and restart the process as the dce user
+if [ "$(id -u)" = '0' ]; then
+  chown -R dce:dce /out
+  exec su-exec dce "$0" "$@"
+fi
+
+exec ./DiscordChatExporter.Cli "$@"