Add readme to store installer

bahmcloud_store_installer/README.md

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+# Bahmcloud Store Installer (Add-on)
+
+This Home Assistant Supervisor add-on installs or updates the **Bahmcloud Store** custom component into:
+
+`/config/custom_components/bahmcloud_store`
+
+## What it does
+- Downloads a ZIP archive of the Bahmcloud Store repository
+- Extracts `custom_components/bahmcloud_store`
+- Copies it into Home Assistant's `/config/custom_components/`
+
+## Configuration
+
+Option | Description | Default
+---|---|---
+`store_component_zip` | ZIP URL of the Bahmcloud Store repository | `https://git.bahmcloud.de/bahmcloud/bahmcloud_store/archive/main.zip`
+
+## Usage
+1. Install the add-on
+2. Start it once (it runs one-shot)
+3. Restart Home Assistant
+
+## Troubleshooting
+- If you update the store component, you must restart Home Assistant afterwards.
+- If the ZIP URL changes, adjust `store_component_zip` in the add-on configuration.