add readme

Author: JeremyEspresso

README.md

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+# swift-h3
+
+Swift bindings for [Uber's H3](https://github.com/uber/h3) library – a fast, hexagonal hierarchical geospatial indexing system.
+
+This package provides native Swift access to core H3 functionality by wrapping the C library via Swift Package Manager.
+
+---
+
+## Features
+- [x] Indexing API
+- [x] Inspection API
+- [x] Traversal API
+- [x] Hierarchy API
+- [x] Regions API
+- [ ] Directed edges API
+- [ ] Vertexes API
+- [ ] Miscellaneous
+---
+
+## Installation
+
+### Swift Package Manager
+
+Add this to your `Package.swift`:
+
+```swift
+.package(url: "https://github.com/JeremyEspresso/swift-h3.git", from: "1.0.0")
+```
+
+## 🔨 Development
+
+This package wraps the H3 C library via submodule.
+
+Clone with submodules:
+
+```bash
+git clone --recurse-submodules https://github.com/JeremyEspresso/swift-h3.git
+```
+
+Then build:
+```bash
+swift build
+swift test
+```