Add README

README.md

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+# SwiftLog OSLog
+A OSLog ([unified logging][unfied-logging]) [backend implementation][backend] for [SwiftLog (swift-log)][swift-log].
+It maps the `label` parameter of [SwiftLog (swift-log) to the `subsystem` and
+`category` parameter of `OSLog`. It even allows the use of the bundle
+identifier - if any  as a value for the `subsystem` parameter.
+
+[unified-logging]: https://developer.apple.com/documentation/os/logging
+[backend]: https://swiftpackageindex.com/apple/swift-log/1.10.1/documentation/logging
+[swift-log]: https://github.com/apple/swift-log
+
+## Installation
+To use this library in your project, add it to the package dependencies:
+
+```swift
+.package(url: "https://github.com/astzweig/swift-log-oslog", from: "1.0.0")
+```
+
+and add it as a dependency on the specific target:
+
+```swift
+.target(
+	name: "YourTarget",
+	dependencies: [
+		.product(name: "LoggingOSLog", package: "swift-log-oslog")
+	]
+)
+```
+
+### Basic Usage
+```swift
+// Import the logging API and this backend implementation
+import Logging
+#if canImport(Darwin)
+import LoggingOSLog
+#endif
+
+// Later, in your application initialization code
+func init() {
+	// ...
+	#if canImport(Darwin)
+	LoggingSystem.bootstrap(LoggingOSLog.init)
+	#endif
+	
+	// Start creating loggers
+	let loggers: [String: Logger] = [
+		"main": Logger(label: "com.example.yourapp.Main"),
+		"mail": Logger(label: "com.example.yourapp.Mail System"),
+	]
+}
+```