Add code readme

Author: Isaac

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to AI assistants when working with code in this repository.
+
+## Build
+The app is built using Bazel.
+
+## Code Style Guidelines
+- **Naming**: PascalCase for types, camelCase for variables/methods
+- **Imports**: Group and sort imports at the top of files
+- **Error Handling**: Properly handle errors with appropriate redaction of sensitive data
+- **Formatting**: Use standard Swift/Objective-C formatting and spacing
+- **Types**: Prefer strong typing and explicit type annotations where needed
+- **Documentation**: Document public APIs with comments
+
+## Project Structure
+- Core launch and application extensions code is in `Telegram/` directory
+- Most code is organized into libraries in `submodules/`
+- External code is located in `third-party/`
+- No tests are used at the moment