website: Added reference to source Dockerfile for images

Change-Id: I2443f2205b023e292181f8a4288dfa48bc671515
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/28870
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: Jason Lowe-Power <power.jg@gmail.com>
1 file changed