Link referenced Dockerfile in the /scripts/README.md
I linked the Dockerfile that the README.md in /scripts/ was referencing.
Closes
This directory contains files required to build Bazel's website.
The website is built using Jekyll running inside a Docker container.
-See the `Dockerfile` for instructions how to test this on your local machine.
+See the [`Dockerfile`](https://github.com/bazelbuild/bazel/blob/HEAD/scripts/docs/Dockerfile) for instructions how to test this on your local machine.
