docs(docker): add docker.md (#227)

script/docker-entrypoint.sh

@@ -0,0 +1,20 @@
+#!/bin/sh
+set -eu
+
+[ -n "${UMASK:-}" ] && umask "$UMASK"
+
+if [ "$(id -u)" = '0' ]; then
+  PUID=${PUID:-1000}
+  PGID=${PGID:-1000}
+
+  DATA_DIRS="/app /usr/local/bin"
+  for DIR in ${DATA_DIRS}; do
+    if [ -d "$DIR" ]; then
+      chown -R "${PUID}:${PGID}" "$DIR" || true
+    fi
+  done
+
+  exec gosu "${PUID}:${PGID}" "$@"
+else
+  exec "$@"
+fi