Encourage user to run e2e by run-e2e-tests.sh instead of make e2e_test in doc

As part of the Kubernetes shim there is also a set of tests defined called the end to end tests. These tests are more complex to execute as they require some extra tools to be installed. Execution, and a pass, of the tests is strongly recommended for changes to the Kubernetes shim repository. They can be executed locally via make e2e_test.

We should encourage user to run e2e by `run-e2e-test.sh` instead of `make e2e_test` as make e2e_test won't setup k8s testing environment.