add example to README

README.md

@@ -1,3 +1,90 @@
 # app
 
 app is a simple and lightweight app lifecycle management library.
+
+## Example
+
+Keep your `main.go` as simple as possible, all it's responsible for is creating the lifecycle, defining a default logger, and orchestrating setup and teardown.
+
+**main.go**
+
+```go
+package main
+
+import (
+	"context"
+	"fmt"
+	"log/slog"
+
+	"gitea.auvem.com/go-toolkit/app"
+)
+
+func main() {
+	// Create a new lifecycle, defaulting to no printed logs
+	lifecycle := app.NewLifecycle().WithLogger(slog.New(slog.DiscardHandler))
+	defer func() {
+		if err := lifecycle.Teardown(); err != nil {
+			fmt.Println("Error during shutdown", err)
+		}
+	}()
+
+	// Encodes the lifecycle into a context to be used downstream
+	ctx := lifecycle.Context(context.Background())
+
+	// Off to you, call your entrypoint here.
+	Hello(ctx)
+}
+```
+
+Now, let's define a basic logging module and handle loading that module.
+
+**logger.go**
+
+```go
+package main
+
+import (
+	"log/slog"
+
+	"gitea.auvem.com/go-toolkit/app"
+)
+
+func ModuleLog(setDefault bool) *app.Module {
+	return app.NewModule("logger", app.ModuleOpts{
+		Setup: func(m *app.Module) error {
+			handler := slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{})
+			if setDefault {
+				slog.SetDefault(handler)
+			}
+
+			m.Lifecycle().WithLogger(handler)
+		}
+	})
+}
+```
+
+Logging can, however, be somewhat of a complex operation in itself, so I'd highly recommend checking out my [applog](https://gitea.auvem.com/go-toolkit/applog) project, which features tight integration with this app.
+
+Finally, lets put our new lifecycle (and logger) to work!
+
+**hello.go**
+
+```go
+package main
+
+import (
+	"context"
+
+	"gitea.auvem.com/go-toolkit/app"
+)
+
+func Hello(ctx context.Context) {
+	app := app.LifecycleFromContext(ctx)
+	if app == nil {
+		panic("hello must run within an app lifecycle")
+	}
+	lifecycle.Require(ModuleLog(true))
+
+	app.Logger().Info("Hello world!", "foo", "bar")
+}
+```