docs: add readme and example of template.json

README.md

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+# sbrs — sing-box rules sync
+
+A containerized Rust utility to synchronize and self-host remote rule sets for `sing-box`.
+
+## Core Workflow
+
+1.  **Reads** a source JSON configuration (`config/template.json`) containing remote URLs (e.g., from GitHub).
+2.  **Downloads** all rule files specified in the source config to a local directory (for example, `./rules`).
+3.  **Cleans up** stale rule files from the local directory that are no longer present in the source config.
+4.  **Generates** a new, client-facing configuration (`config/default.json`) where all remote URLs are rewritten to point to a self-hosted domain.
+
+The original `template.json` is never modified by this application.
+
+Upon container start, the utility performs an initial synchronization immediately and then sets up a cron job for subsequent, scheduled runs.
+
+## Prerequisites
+
+-   Docker
+-   Docker Compose
+
+## Usage via Docker
+
+**1. Example of possible directory structure**
+
+Create the following directory structure in your project root before the first run:
+
+```
+.
+├── config/
+│   └── template.json	# Your input config with original URLs
+├── rules/              # Empty directory for downloaded rule files
+├── docker/
+│   ├── Dockerfile
+│   └── entrypoint.sh
+└── docker-compose.yml
+```
+*Note: `config/default.json` will be generated by the application on the first run.*
+
+**2. Configuration**
+
+Edit `docker-compose.yml` to set the required environment variables:
+
+-   `PUID`/`PGID`: Set to your host user's ID (`id -u`) and group ID (`id -g`) to prevent volume permission issues.
+-   `DOMAIN`: The public domain that will serve the rule files (e.g., `rules.mydomain.com`).
+-   `RULE_PATH`: The path on the domain where the files are located (e.g., `/` or `/files`).
+-   `TZ`: The timezone for container logs (e.g., `Etc/UTC`).
+-   `CRON_SCHEDULE`: The schedule for the sync task.
+
+**3. Run the Service**
+
+```bash
+# Build the image and start the service in detached mode
+docker-compose up --build -d
+```
+
+The service will run the sync task immediately upon starting and then again on the schedule defined by `CRON_SCHEDULE`.
+
+### Common Commands
+
+```bash
+# View live logs
+docker-compose logs -f
+
+# Trigger a manual sync immediately (without restarting)
+docker-compose exec sbrs entrypoint.sh manual
+
+# Stop and remove the container
+docker-compose down
+```
+
+## Local Development
+
+Requires the [Rust toolchain](https://rustup.rs/).
+
+**1. Build**
+```bash
+cargo build --release
+```
+
+**2. Run**
+
+All arguments are required.
+
+```bash
+./target/release/sbrs \
+    --input-config ./config/template.json \
+    --rules-dir ./rules \
+    --output-config ./config/default.json \
+    --domain my.server.com \
+    --rule-path rules
+```