Add a flaky test section to contributor guide.

Signed-off-by: Siyuan Zhang <[email protected]>

CONTRIBUTING.md

@@ -43,6 +43,34 @@ If any of aforementioned labels don't have unassigned issues, please [contact] o
 [maintainers]: https://github.com/etcd-io/etcd/blob/main/OWNERS
 [priority/important]: https://github.com/search?type=issues&q=org%3Aetcd-io+state%3Aopen++label%3A%22priority%2Fimportant%22
 
+### Flaky Tests
+
+The project could always use some help to deflake flaky tests. [These](https://github.com/etcd-io/etcd/issues?q=is%3Aissue+is%3Aopen+label%3Atype%2Fflake) are the currently open flaky test issues.
+
+For more, because etcd uses Kubernetes' prow infrastructure to run CI jobs, the past test results can be viewed at [testgrid](https://testgrid.k8s.io/sig-etcd).
+
+| Tests  | Status  |
+| -----  | ------  |
+| periodics e2e-amd64  | [![sig-etcd-periodics/ci-etcd-e2e-amd64](https://testgrid.k8s.io/q/summary/sig-etcd-periodics/ci-etcd-e2e-amd64/tests_status?style=svg)](https://testgrid.k8s.io/q/summary/sig-etcd-periodics/ci-etcd-e2e-amd64)  |
+| presubmit build      | [![sig-etcd-presubmits/pull-etcd-build](https://testgrid.k8s.io/q/summary/sig-etcd-presubmits/pull-etcd-build/tests_status?style=svg)](https://testgrid.k8s.io/q/summary/sig-etcd-presubmits/pull-etcd-build)  |
+| presubmit e2e-amd64  | [![sig-etcd-presubmits/pull-etcd-e2e-amd64](https://testgrid.k8s.io/q/summary/sig-etcd-presubmits/pull-etcd-e2e-amd64/tests_status?style=svg)](https://testgrid.k8s.io/q/summary/sig-etcd-presubmits/pull-etcd-e2e-amd64)  |
+| presubmit unit-test  | [![sig-etcd-presubmits/pull-etcd-unit-test](https://testgrid.k8s.io/q/summary/sig-etcd-presubmits/pull-etcd-unit-test/tests_status?style=svg)](https://testgrid.k8s.io/q/summary/sig-etcd-presubmits/pull-etcd-unit-test)  |
+| presubmit verify     | [![sig-etcd-presubmits/pull-etcd-verify](https://testgrid.k8s.io/q/summary/sig-etcd-presubmits/pull-etcd-verify/tests_status?style=svg)](https://testgrid.k8s.io/q/summary/sig-etcd-presubmits/pull-etcd-verify)  |
+| postsubmit build     | [![sig-etcd-postsubmits/post-etcd-build](https://testgrid.k8s.io/q/summary/sig-etcd-postsubmits/post-etcd-build/tests_status?style=svg)](https://testgrid.k8s.io/q/summary/sig-etcd-postsubmits/post-etcd-build)  |
+
+If you find any flaky tests on testgrid, please
+
+1. open an issue with the `type/flake` label.
+2. try to reproduce the flaky test on your machine via `stress`, for example to reproduce the failure of `TestPeriodicSkipRevNotChange`:
+```bash
+cd server/etcdserver/api/v3compactor
+# compile the test
+go test -v -c -count 1 -run "^TestPeriodicSkipRevNotChange$"
+# run the compiled test file using stress
+stress -p=8 ./v3compactor.test
+```
+3. fix it.
+
 ## Setup development environment
 
 The etcd project supports two options for development: