Clarify the macOS requirement for container hosts

[qayshp]

What changed

• explain why the BlueBubbles server must run within macOS
• distinguish a native Linux or Windows container from a Linux-hosted macOS VM
• link readers to the existing virtualization and Docker-OSX guides

Why

The server overview said that macOS virtual machines are compatible, but it did not explicitly answer whether BlueBubbles could run as an ordinary Linux or Windows container. That omission made Docker and Podman deployments sound platform-independent even though the server depends on the macOS Messages app, chat.db, AppleScript, and optional macOS-only Private API frameworks.

This clarification makes the deployment boundary explicit: Docker or Podman can host a macOS virtual machine, but BlueBubbles still runs inside the macOS guest.

Impact

Readers can choose an appropriate host setup without mistaking the Docker-OSX path for a native Linux server.

Checks

• git diff --check
• verified both linked documentation targets exist in the repository
• checked the wording against the maintainer explanation on the issue

Fixes BlueBubblesApp/bluebubbles-server#762

[qayshp]

Self-review focused on whether the new deployment guidance sets the right expectations.

[qayshp]

Validation update

• git diff --check origin/master...HEAD passes.
• Both linked documentation targets resolve in the repository.
• The deployment-boundary explanation matches the current server's macOS Messages database, AppleScript, and optional Private API dependencies.
• No runtime or SIP-disabled-machine test is needed for this conceptual clarification.

No documentation screenshot is needed for this change.