feat: support RELATIVE_URL_ROOT (fix #127)

rootfs/usr/local/bin/chromium-browser-sound.sh

@@ -0,0 +1,8 @@
+#!/bin/sh
+
+if [ -z "$ALSADEV" ]; then
+    zenity --error --text "To support audio, please read README.md and run container with --device /dev/snd -e ALSADEV=..."
+    exit 1
+fi
+
+exec /usr/bin/chromium-browser --no-sandbox --alsa-output-device="$ALSADEV" "$@"

rootfs/usr/local/bin/xvfb.sh

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+exec /usr/bin/Xvfb :1 -screen 0 1024x768x16