Add EXPOSE for 80 and 69/udp

This should document the default ports that are opened
by the container for cases like QNAP devices that rely on
that to populate the default ports.

Closes: https://github.com/netbootxyz/netboot.xyz/issues/1409

Dockerfile

@@ -49,6 +49,8 @@ RUN \
 ENV TFTPD_OPTS=''
 ENV NGINX_PORT='80'
 
+EXPOSE 69/udp
+EXPOSE 80
 EXPOSE 3000
 
 COPY root/ /