add OPENHAB_HTTP_PORT to start.sh

[weberjn]

An easy trap to fall in at first start is if the 8080 port is already used (most probably by Tomcat or Wildfly).

I suggest to add a commented hint

# Change this if the port is used by another program
# export OPENHAB_HTTP_PORT=8080
# export OPENHAB_HTTPS_PORT=8083

to start.bat and the analogous to start.bat