Initial commit: add Minecraft plugin updater

Add Dockerfile, main Python script, example config, requirements, and README for a Dockerized Minecraft plugin updater. The updater supports GitHub, Modrinth, and Spigot plugins, automatically checks for updates, downloads new versions, and manages plugin files and state.

README.md

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+# Minecraft Plugin Updater
+
+A Dockerized Python script that automatically checks for and downloads updates for Minecraft plugins from GitHub, Modrinth, and Spigot.
+
+## Features
+- Supports GitHub, Modrinth, and Spigot (via Spiget).
+- Automatically deletes old versions upon update.
+- Configurable check interval.
+- Maintains state to track installed versions.
+
+## Usage
+
+1.  **Create a data directory:**
+    Create a folder on your host machine (e.g., `updater-data`).
+
+2.  **Create configuration:**
+    Copy `config.example.yaml` to your data directory, rename it to `config.yaml`, and edit it with your plugins.
+
+    ```yaml
+    check_interval: 3600
+    plugins:
+      - name: "MyPlugin"
+        source: "github"
+        repo: "user/repo"
+    ```
+
+3.  **Run with Docker:**
+
+    ```bash
+    docker run -d \
+      --name plugin-updater \
+      -v /path/to/updater-data:/data \
+      minecraft-plugin-updater
+    ```
+
+    Plugins will be downloaded to `/path/to/updater-data/plugins`.
+
+## Configuration Options
+
+- **GitHub:**
+  - `source`: "github"
+  - `repo`: "owner/repository"
+  - `asset_regex`: (Optional) Regex to match specific release asset names.
+
+- **Modrinth:**
+  - `source`: "modrinth"
+  - `id`: Project ID or Slug
+  - `loader`: (Optional) e.g., "spigot", "paper"
+  - `game_version`: (Optional) e.g., "1.20.1"
+
+- **Spigot:**
+  - `source`: "spigot"
+  - `id`: Resource ID (found in the URL, e.g., `https://www.spigotmc.org/resources/plugin-name.12345/` -> `12345`)
+