Update instructions for multi-platform docker images.

3. Execute the cross-compiled build helper.

   ```

   xgo --targets=darwin/arm64,darwin/amd64,linux/amd64,linux/arm64,windows/amd64 --trimpath --ldflags "-s -w -X main.version=2.1.0 -X main.commitID=$(git rev-parse --short HEAD 2>/dev/null)" 

github.com/heroiclabs/nakama

   xgo --targets=darwin/arm64,darwin/amd64,linux/amd64,linux/arm64,windows/amd64 --trimpath --ldflags "-s -w -X main.version=2.1.0 -X main.commitID=$(git rev-parse --short HEAD 2>/dev/null)" github.com/heroiclabs/nakama

   ```

   This will build binaries for all target platforms supported officially by Heroic Labs.

With the release generated we can create the official container image.

1. Build the container image.

These steps are one off to install the required build utilities.

1. Ensure you have the Docker Buildx client installed. (https://docs.docker.com/build/architecture/#install-buildx)

2. Create a new builder instance that supports multi-platform builds, and switch to use it.

   ```

   cd build

   docker build "$PWD" --platform "linux/amd64" --file ./Dockerfile --build-arg commit="$(git rev-parse --short HEAD 2>/dev/null)" --build-arg version=2.1.0 -t heroiclabs/nakama:2.1.0

   docker buildx create --name mybuilder --driver docker-container --bootstrap --use

   ```

2. Push the image to the container registry.

These steps are run for each new release.

1. Use an existing builder that supports multi-platform builds.

   ```

   docker tag <CONTAINERID> heroiclabs/nakama:latest

   docker push heroiclabs/nakama:2.1.0

   docker push heroiclabs/nakama:latest

   docker buildx use mybuilder

   ```

2. Build the container image and push to the container registry.

   ```

   cd build

   docker build "$PWD" --platform linux/amd64,linux/arm64 --file ./Dockerfile --build-arg commit="$(git rev-parse --short HEAD 2>/dev/null)" --build-arg version=2.1.0 -t heroiclabs/nakama:2.1.0 -t heroiclabs/nakama:latest --push

   ```

## Build Nakama Image (dSYM)

With the release generated we can also create an official container image which includes debug symbols.

1. Build the container image.

1. Use an existing builder that supports multi-platform builds.

   ```

   cd build

   docker build "$PWD" --platform "linux/amd64" --file ./Dockerfile.dsym --build-arg commit="$(git rev-parse --short HEAD 2>/dev/null)" --build-arg version=2.1.0 -t heroiclabs/nakama-dsym:2.1.0

   docker buildx use mybuilder

   ```

2. Push the image to the container registry.

2. Build the container image and push to the container registry.

   ```

   docker tag <CONTAINERID> heroiclabs/nakama-dsym:latest

   docker push heroiclabs/nakama-dsym:2.1.0

   docker push heroiclabs/nakama-dsym:latest

   cd build

   docker build "$PWD" --platform linux/amd64,linux/arm64 --file ./Dockerfile.dsym --build-arg commit="$(git rev-parse --short HEAD 2>/dev/null)" --build-arg version=2.1.0 -t heroiclabs/nakama-dsym:2.1.0 -t heroiclabs/nakama-dsym:latest --push

   ```

## Build Plugin Builder Image

With the official release image generated we can create a container image to help with Go runtime development.

1. Build the container image.

1. Use an existing builder that supports multi-platform builds.

   ```

   cd build/pluginbuilder

   docker build "$PWD" --platform "linux/amd64" --file ./Dockerfile --build-arg commit="$(git rev-parse --short HEAD 2>/dev/null)" --build-arg version=2.1.0 -t heroiclabs/nakama-pluginbuilder:2.1.0

   docker buildx use mybuilder

   ```

2. Push the image to the container registry.

2. Build the container image.

   ```

   docker tag <CONTAINERID> heroiclabs/nakama-pluginbuilder:latest

   docker push heroiclabs/nakama-pluginbuilder:2.1.0

   docker push heroiclabs/nakama-pluginbuilder:latest

   cd build/pluginbuilder

   docker build "$PWD" --platform linux/amd64,linux/arm64 --file ./Dockerfile --build-arg commit="$(git rev-parse --short HEAD 2>/dev/null)" --build-arg version=2.1.0 -t heroiclabs/nakama-pluginbuilder:2.1.0 -t heroiclabs/nakama-pluginbuilder:latest --push

   ```