Update documentation for migration to prow.

Signed-off-by: James Blair <[email protected]>

CONTRIBUTING.md

@@ -175,7 +175,8 @@ releases.
 
 ## Get your pull request reviewed
 
-Before requesting review please ensure that all GitHub checks were successful.
+Before requesting review please ensure that all GitHub and Prow checks are successful. In some cases your pull request may have the label `needs-ok-to-test`. If so an `etcd-io` organisation member will leave a comment on your pull request with `/ok-to-test` to trigger all checks to be run.
+
 It might happen that some unrelated tests on your PR are failing, due to their flakiness.
 In such cases please [file an issue] to deflake the problematic test and ask one of [maintainers] to rerun the tests.
 

Documentation/contributor-guide/triage_prs.md

@@ -16,6 +16,10 @@ Following are a few example searches on PR for convenience:
 
 These guidelines serve as a primary document for managing PRs in `etcd`. Everyone is welcome to help manage PRs but the work and responsibilities discussed in this document are created with `etcd` maintainers and active contributors in mind.
 
+## Ensure tests are run
+
+The etcd project use Kubernetes Prow and GitHub Actions to run tests. To ensure all required tests run if a pull request is ready for testing and still has the `needs-ok-to-test` label then please comment on the pull request `/ok-to-test`.
+
 ## Handle inactive PRs
 Poke PR owner if review comments are not addressed in 15 days. If the PR owner does not reply in 90 days, update the PR with a new commit if possible. If not, inactive PR should be closed after 180 days.