Add instructions for using docker to regen derived files

README.md

@@ -167,7 +167,21 @@ Some of the Trillian Go code is autogenerated from other files:
    golang.org/x/tools/cmd/stringer`).
 
 Re-generating mock or protobuffer files is only needed if you're changing
-the original files; if you do, you'll need to install the prerequisites:
+the original files. The recommended way to do this is by using the Docker
+image used by the Cloud Build:
+
+```shell
+docker build -f ./integration/cloudbuild/testbase/Dockerfile -t trillian-builder .
+docker run -it --mount type=bind,src="$(pwd)",target=/src trillian-builder /bin/bash -c "cd /src; ./scripts/install_deps.sh; go generate -x ./..."
+```
+
+These commands first create a docker image from the Dockerfile in this repo, and
+then launch a container based on this image with the local directory mounted. The
+correct versions of the tools are determined using the `go.mod` file in this repo,
+and these tools are installed. Finally, all of the generated files are regenerated
+and Docker exits.
+
+Alternatively, you can install the prerequisites locally:
 
   - a series of tools, using `go install` to ensure that the versions are
     compatible and tested:

scripts/install_deps.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+#
+# Installs the dependencies required to build this repo.
+set -eu
+
+main() {
+  go install github.com/golang/mock/mockgen
+  go install google.golang.org/protobuf/proto
+  go install google.golang.org/protobuf/cmd/protoc-gen-go
+  go install google.golang.org/grpc/cmd/protoc-gen-go-grpc
+  go install github.com/pseudomuto/protoc-gen-doc/cmd/protoc-gen-doc
+  go install golang.org/x/tools/cmd/stringer
+}
+
+main