Update readme with more details

Author: florianpircher

README.md

@@ -1 +1,26 @@
-# Swift Package for libgit2
+# Clibgit2 – Swift Package for libgit2
+
+This is a Swift package for linking to the [libgit2](https://libgit2.org) library.
+macOS is currently the only supported platform given the build configuration in the package manifest.
+
+This package does not provide any Swift API overlay and instead just offers access to the C API.
+
+## Usage
+
+Include this package as a dependency like so:
+
+```swift
+let package = Package(
+	// ...
+	platforms: [
+		.macOS(.v11),
+	],
+	// ...
+	dependencies: [
+		.package(url: "https://github.com/Formkunft/Clibgit2", from: "1.9.0"),
+	],
+	// ...
+)
+```
+
+The version numbers of this package follow the version numbers of libgit2.