doc

Signed-off-by: Derek Wang <[email protected]>

README.md

@@ -18,3 +18,25 @@ Source Transformer, Functions, Sinks or SideInputs in Golang.
 `make test` - Run the tests.
 `make proto`- Regenerate the protobuf files from the [proto files](https://github.com/numaproj/numaflow/tree/main/pkg/apis/proto) defined in [numaproj/numaflow](https://github.com/numaproj/numaflow) repository.
 `make proto ORG=xxx PROJECT=xxx BRANCH=xxx` - Regenerate the protobuf files from specified github repository. Default values: `ORG=numaproj PROJECT=numaflow BRANCH=main`
+
+### Proto File Changes
+
+The source proto files are located at [numaflow](https://github.com/numaproj/numaflow/tree/main/pkg/apis/proto) repository, so any proto file change should start from numaflow repository change, and Go should always be the 1st SDK to update.
+
+This means, usually there will be two PRs to update gRPC contracts, one in `numaflow` for proto file changes, the other one in `numaflow-go` to update the detailed implementation. There is one trick to unblock the code change in `numaflow-go` to run codegen for proto files, before the proto file change PR is merged in `numaflow` repository:
+
+```shell
+make proto ORG=xxx BRANCH=xxx
+```
+
+This will run proto gen with the source files defined in your own repository and branch.
+
+For example:
+
+```shell
+# Try to fetch proto files defined in branch "proto-chg" of https://github.com/anyone/numaflow
+make proto ORG=anyone BRANCH=proto-chg
+
+# Try to fetch proto files defined in branch "my-change" of https://github.com/numaproj/numaflow
+make proto BRANCH=my-change
+```