Update README

README.md

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 # OpenWeatherWidget
 
-Tiny desktop widget for weather updates using the OpenWeatherMap API
+Tiny desktop widget for weather updates using the [OpenWeatherMap](https://openweathermap.org) API.
+
+## Status
+⚠️ Work in progress - not ready for general use.
+
+## Configuration
+The widget reads configuration from:
+
+```
+~/.config/candywidgets/openweathermap.toml
+````
+
+Example:
+
+```toml
+[general]
+api_key = "your_api_key_here" # get a free API key from https://openweathermap.org
+city_id = "your_city_id_here" # Find at https://openweathermap.org/find?
+units="metric"
+````
+⚠️ WIP - Full configuration format will be released later.
+
+## API
+
+* Currently uses **Weather API v2.5**.
+* While this API is deprecated in favor of [One Call API 3.0](https://openweathermap.org/api/one-call-3), it still works as of today.
+* One Call API 3.0 is free for up to 1000 API calls per day, but requires payment information for subscription.
+* Migration to v3.0 may be considered later.
+
+## To-do  
+
+- [ ] TOML configuration file  
+- [ ] Fetch and parse weather data from openweathermap.org
+- [ ] Complete configuration  
+- [ ] CLI args  
+- [ ] GUI - [iced](https://book.iced.rs/)  
+- [ ] Migrate to One Call API 3.0