Update CONTRIBUTING.md for how to set up a Docker builder (#4668)

Co-authored-by: Frank Elsinga <frank@elsinga.de>

CONTRIBUTING.md

@@ -490,3 +490,28 @@ We have a few procedures we follow. These are documented here:
   
   </p>
   </details>
+
+### Set up a Docker Builder
+
+- amd64, armv7 using local.
+- arm64 using remote arm64 cpu, as the emulator is too slow and can no longer pass the `npm ci` command.
+   1. Add the public key to the remote server.
+   2. Add the remote context. The remote machine must be arm64 and installed Docker CE. 
+      ```
+      docker context create oracle-arm64-jp --docker "host=ssh://root@100.107.174.88"
+      ```
+   3. Create a new builder.
+      ```
+      docker buildx create --name kuma-builder --platform linux/amd64,linux/arm/v7
+      docker buildx use kuma-builder
+      docker buildx inspect --bootstrap
+      ```
+   4. Append the remote context to the builder.
+      ```
+      docker buildx create --append --name kuma-builder --platform linux/arm64 oracle-arm64-jp
+      ```
+   5. Verify the builder and check if the builder is using `kuma-builder`.
+      ```
+      docker buildx inspect kuma-builder
+      docker buildx ls
+      ```