docs: add DVSwitch Filesystem-Mirror.md to bookworm

DVSwitch Filesystem-Mirror.md

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+# DVSwitch Filesystem-Mirror
+
+## Purpose
+
+This repository is a **filesystem-mirror** — a pure representation of the
+DVSwitch package contents as they would appear on a Debian Linux filesystem.
+
+Unlike traditional packaging repositories that carry debian packaging metadata
+(`DEBIAN/`, control files, maintainer scripts), this repository strips all
+packaging metadata and maps directly to the target filesystem paths.
+
+## Structure
+
+Every file is placed at its intended target path, rooted at the repository root:
+
+```
+etc/          → /etc/          (configuration files, logrotate configs)
+lib/          → /lib/          (systemd service units)
+opt/          → /opt/          (binaries, application data)
+usr/          → /usr/          (scripts, libraries, shared data)
+var/          → /var/          (runtime data, language files, talkgroup lists)
+```
+
+## Architecture-Specific Binaries
+
+Architecture-specific ELF binaries follow a `.arch` suffix convention:
+
+- `foo.amd64` — x86_64
+- `foo.arm64` — aarch64
+- `foo.armhf` — ARM hard-float
+- `foo.i386` — x86
+
+The **amd64** variant is authoritative for configuration and data files;
+other architectures contribute only architecture-specific ELF binaries.
+
+## Branches
+
+| Branch | Purpose |
+|--------|---------|
+| `bookworm` | Filesystem-mirror for Debian 12 bookworm |
+| `development` | Development branch (tracks bookworm) |
+
+## Origin
+
+Binaries and configuration files in this repository were extracted from
+Debian `.deb` packages built by [DVSwitch](https://github.com/DVSwitch).