docs: add notedeck_columns readme

Signed-off-by: William Casarin <jb55@jb55.com>

crates/notedeck_columns/README.md

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+# NoteDeck Columns
+
+A TweetDeck-style multi-column interface for Nostr built with Rust and egui.
+
+## Overview
+
+NoteDeck Columns is a specialized UI component of the NoteDeck Nostr client that provides a TweetDeck-inspired multi-column layout for browsing Nostr content. It allows users to create customizable "decks" with multiple columns, each showing different types of Nostr content (home timeline, notifications, hashtags, profiles, etc.).
+
+## Features
+
+- **Multi-column layout**: View different Nostr content types side by side
+- **Customizable decks**: Create and customize multiple decks for different use cases
+- **Column types**:
+  - Universe (global feed)
+  - Contact lists (follows)
+  - Profiles
+  - Notifications
+  - Hashtags
+  - Threads
+  - Search results
+  - Algorithmic feeds (e.g., last notes per pubkey)
+- **Interactions**: Post, reply, quote, and zap notes
+- **Media support**: View and upload images
+- **Multiple accounts**: Switch between multiple Nostr accounts
+
+## Getting Started
+
+NoteDeck Columns is part of the larger NoteDeck ecosystem. To use it:
+
+1. Clone the NoteDeck repository
+2. Build the project with Cargo
+3. Run NoteDeck and select the Columns interface
+
+See the [DEVELOPER.md](DEVELOPER.md) file for detailed setup instructions.
+
+## Architecture
+
+NoteDeck Columns is built using:
+
+- **Rust**: For performance and type safety
+- **egui**: For the UI rendering
+- **nostrdb**: For Nostr data storage and retrieval
+- **enostr**: For Nostr protocol communication
+
+The codebase is organized around the concept of timelines, views, and decks, with a column-based UI architecture.
+
+## Contributing
+
+Contributions are welcome! Please see [DEVELOPER.md](DEVELOPER.md) for information on how to set up your development environment and contribute to the project.
+
+## License
+
+NoteDeck Columns is licensed under the [GPL v3](LICENSE).