Add docs for CRI validation test suites

Signed-off-by: Pengfei Ni <feiskyer@gmail.com>

contributors/devel/cri-validation.md

@@ -0,0 +1,50 @@
+# CRI Validation Testing
+
+CRI validation testing provides a serial of common validation test suites for Kubelet CRI (_Container Runtime Interface_).
+
+It helps container runtime maintainers to validate their runtime when integrating with kubelet CRI.
+
+*Note: No kubelet is running. The test suites run directly targeting the shim of container runtime.*
+
+*Note: CRI validation testing is alpha and maintained at [cri-tools](https://github.com/kubernetes-incubator/cri-tools) repo.*
+
+## Install
+
+The test suites could be installed easily via `go get` command:
+
+```sh
+go get github.com/kubernetes-incubator/cri-tools/cmd/critest
+```
+
+Then `critest` binary could be found in `$GOPATH/bin`.
+
+*Note: ensure GO is installed and GOPATH is set before installing critest.*
+
+## Running tests
+
+Before running the tests, ensure the shim of CRI container runtime is running and kubelet is stopped.
+
+Run:
+
+```sh
+critest validation
+```
+
+This will
+
+- Connect to the shim of CRI container runtime
+- Run the tests using `ginkgo`
+- Output the test results to STDOUT
+
+critest connects to `/var/run/dockershim.sock` by default. For other runtimes, the endpoint could be set in two ways:
+
+- By setting flags `--runtime-endpoint` and `--image-endpoint`
+- By setting environment variables `CRI_RUNTIME_ENDPOINT` and `CRI_IMAGE_ENDPOINT`
+
+## Additional options
+
+- `--focus`, `-f`: Only run the tests that match the regular expression.
+- -`-ginkgo-flags`, `-g`: Space-separated list of arguments to pass to Ginkgo test runner.
+- `--image-endpoint`, `-i`: Set the endpoint of image service. Same with runtime-endpoint if not specified.
+- `--runtime-endpoint`, `-r`: Set the endpoint of runtime service. Default to `/var/run/dockershim.sock`.
+- `--skip`, `-s`: Skip the tests that match the regular expression.