Update k8s-bench README and run-eval-loop.sh

[noahlwest]

Update README to include info about run-eval-loop.sh (preferred script for running evals)

• We can also remove run-evals.sh, analyze-evals.sh, and remove/update their respective make targets if we want to just provide 1 way of running evals (run-eval-loop.sh). Right now I'm leaving them, but indicated that run-eval-loop is the preferred method.
• run-eval-loop.sh no longer relies on the run evals make target. Also changed default values so it acts more as a stand-in for that make target.
• removed some excessive comments and print statements