Add create-basis/process example to tools.build docs

[seancorfield]

Per discussion on Slack about using clojure.tools.build to run tests that need a particular classpath, including the test runner itself, Alex said "you can use a combo of create-basis, java-command, and process to execute it".

It would be great if the tools.build guide had an example of doing this with Cognitect's test-runner to provide a canonical example of how to do this in a build script (where the build script is invoked as the only dependency via -T).