docs: Update README with Docker image generation documentation

[Copilot]

Added comprehensive Docker image generation documentation to the main README covering all four core networking components as requested in the issue.

Changes Made

Added a new "Docker Image Generation" section to README.md that includes:

Prerequisites

• Docker or Podman installation requirements
• Multi-platform build setup instructions

Component-Specific Build Commands

Documentation for building Docker images for each of the four requested components:

1. Container Network Service (CNS)

make cns-image
make cns-image-name-and-tag

2. Container Network Interface (CNI)

make cni-image
make cni-image-name-and-tag

3. Network Policy Manager (NPM)

make npm-image
make npm-image-name-and-tag

4. Azure IP Address Management (Azure-IPAM)

make azure-ipam-image
make azure-ipam-image-name-and-tag

Advanced Features

• Customization options: Platform targeting, custom registries, container builder selection
• Image operations: Push, pull, and multi-platform manifest building
• Working examples: All commands tested and verified

Example Usage

# Build for different architecture
PLATFORM=linux/arm64 make cns-image

# Use custom registry
IMAGE_REGISTRY=myregistry.azurecr.io make cns-image

# Use Podman instead of Docker
CONTAINER_BUILDER=podman make cns-image

The documentation follows the existing repository style and provides clear, actionable instructions for developers who need to build container images for these components.

Fixes #3722.

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[jpayne3506]

@copilot combine make recipes documentation to be generic

[Copilot]

@copilot combine make recipes documentation to be generic

Made the documentation generic with a standardized pattern that applies to all components. The documentation now uses <component>-image format and lists all available components instead of having separate sections for each one. This makes it more maintainable and concise. See commit cecb16b.

[jpayne3506]

@copilot move these changes to ./doc/README.md

[Copilot]

@copilot move these changes to ./doc/README.md

Moved the Docker image generation documentation from the main README.md to doc/README.md as requested. The main README now contains a simple reference to the detailed documentation. See commit 9aadc9e.

[jpayne3506]

@copilot I meant docs/README.md

[Copilot]

@copilot I meant docs/README.md

Moved the Docker image generation documentation to docs/README.md as requested. The content is now integrated into the existing docs/README.md file and the main README.md reference has been updated accordingly. See commit f99a9be.

[Copilot]

Pull Request Overview

This PR adds comprehensive documentation for Docker image generation in the repository, detailing component-specific build commands, prerequisites, and customization options.

• Added a new "Docker Image Generation" section to docs/README.md covering prerequisites, available components, generic build patterns, example usage, and customization.
• Updated the top-level README.md to reference the new Docker documentation.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
docs/README.md	New section documenting Docker image generation, build patterns, and component-specific commands for networking.
README.md	Added a link reference to the Docker image generation documentation in docs/README.md.

Comments suppressed due to low confidence (1)

docs/README.md:22

• The 'Available Components' section lists 'acncli' and 'ipv6-hp-bpf', but the PR description mentions only four core components. Consider clarifying whether these additional components are part of the core set or updating the documentation to match the intended scope.

+- **acncli** - CNI manager

[jpayne3506]

/azp run Azure Container Networking PR

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jpayne3506]

@copilot, document how GOOS=windows impacts image generation

[Copilot]

@copilot, document how GOOS=windows impacts image generation

Added comprehensive Windows image generation documentation covering how GOOS impacts the build process, including cross-compilation behavior, Docker multi-stage targeting, and component-specific considerations. See commit 7a96168.

[NihaNallappagari]

Thanks for updating the readme @jpayne3506

[jpayne3506]

/azp run Azure Container Networking PR

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[rbtr]

remove - GOOS is extracted by parsing PLATFORM and should not be set separately

[rbtr]

@copilot continue removing documentation of GOOS

[Copilot]

Removed all GOOS documentation from docs/README.md as requested. The build system automatically extracts GOOS from the PLATFORM variable, so users only need to specify PLATFORM. See commit f0767b3.

[jpayne3506]

I interpreted

azure-container-networking/Makefile

Line 225 in 4aa36ae

OS ?= $(GOOS)

as we need to override the default for GOOS to change OS. Should we be instead manually overwriting OS?

[rbtr]

well, i know i wrote code to parse the platform in to OS/ARCH somewhere, at some point. but you're right, that's not what's happening here now. i think especially for the container builds we should do it.
maybe we default platform as PLATFORM ?= $GOOS/$GOARCH to pick up the host platfom. but if it is set then we should parse $OS and $ARCH out of it, and then set any go invocation GOOS and GOARCH to those.