Expand Docker documentation

[perennialtech]

Expand Docker documentation

This PR mostly expands on Docker-related documentation for Redlib. Configuration using an .env file for Docker deployments is now covered.

Some formatting changes have also been made in the README (headings and admonitions).

An error in compose.yaml that causes Docker Compose deployments to break has also been fixed (see last bullet point).

Change summary

As a quick summary of changes:

• Modified Docker CLI commands in README.md as well as values in compose.yaml to explicitly specify the latest tag for the Redlib image.

README.md

• Added a new section covering Docker Compose deployments.

• Added documentation covering the use of a .env file to configure Redlib using environment variables for Docker deployments.

• Added a short section on networking considerations for Docker deployments behind a reverse proxy.

• Fixed formatting for admonitions in the README. A line break now appears between the title and the rest of the admonition text.

• Separated configuration into a subsection under Deployment to better accommodate the new section for configuration when using Docker.

compose.yaml

• Prefixed the arm64 and armv7 images in compose.yaml with image: so that it's in line with latest image.

• Changed the name of the Redlib service from web to redlib.

• Changed seccomp="seccomp-redlib.json" to seccomp=seccomp-redlib.json to fix an error about the seccomp profile not being found when deploying using Docker Compose.