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>
diff --git a/_pages/documentation/general_docs/building/index.md b/_pages/documentation/general_docs/building/index.md
index ddc08bd..672dceb 100644
--- a/_pages/documentation/general_docs/building/index.md
+++ b/_pages/documentation/general_docs/building/index.md
@@ -63,15 +63,19 @@
 
 Ubuntu 18.04 with all optional dependencies (Python 2):
 [gcr.io/gem5-test/ubuntu-18.04_all-dependencies](
-https://gcr.io/gem5-test/ubuntu-18.04_all-dependencies).
+https://gcr.io/gem5-test/ubuntu-18.04_all-dependencies) ([source Dockerfile](
+https://gem5.googlesource.com/public/gem5/+/refs/heads/master/util/dockerfiles/ubuntu-18.04_all-dependencies/Dockerfile>)).
 
 Ubuntu 18.04 with the minimum set of dependencies (Python 2):
 [gcr.io/gem5-test/ubuntu-18.04_min-dependencies](
-https://gcr.io/gem5-test/ubuntu-18.04_min-dependencies).
+https://gcr.io/gem5-test/ubuntu-18.04_min-dependencies) ([source Dockerfile](
+https://gem5.googlesource.com/public/gem5/+/refs/heads/master/util/dockerfiles/ubuntu-18.04_min-dependencies/Dockerfile>)).
+
 
 Ubuntu 20.04 with all optional dependencies (Python 3):
 [gcr.io/gem5-test/ubuntu-20.04_all-dependencies](
-https://gcr.io/gem5-test/ubuntu-20.04_all-dependencies).
+https://gcr.io/gem5-test/ubuntu-20.04_all-dependencies) ([source Dockerfile](
+https://gem5.googlesource.com/public/gem5/+/refs/heads/master/util/dockerfiles/ubuntu-20.04_all-dependencies/Dockerfile>)).
 
 To obtain a docker image: