docs: expand deployment asset overview

[ming1523]

Summary

• expand deployment/README.md from a one-line overview into a usable deployment entrypoint
• document the purpose of Dockerfile, e2e-client.Dockerfile, and docker-compose.yml
• add minimal build and docker compose usage examples from the repository root
• clarify that Kubernetes manifests are not currently stored in deployment/

Why

Compared with other infrastructure repositories, fuel-core already ships container assets but the deployment directory did not explain how they fit together. This makes the repository harder to approach for operators and contributors trying to understand the container-based workflow.

Validation

• verified all referenced files exist in the current tree
• docs-only change, no runtime behavior changed

This is a docs-only change. The no changelog label seems appropriate if maintainers agree.

[cursor]

PR Summary

Low Risk
Docs-only update with no changes to runtime behavior; risk is limited to potential confusion if instructions drift from the actual Docker assets.

Overview
Expands deployment/README.md from a one-line note into a short guide describing the purpose of the fuel-core and fuel-core-e2e-client container build assets.

Adds basic usage examples for building the node and e2e client images and running the node via docker compose, and clarifies that Kubernetes manifests are not included here (linking to operator docs).

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