docs: add graceful shtdown example

https://github.com/gin-gonic/autotls/issues/12

README.md

@@ -65,3 +65,39 @@ func main() {
   log.Fatal(autotls.RunWithManager(r, &m))
 }
 ```
+
+example usage for graceful shutdown with custom context.
+
+```go
+package main
+
+import (
+  "context"
+  "log"
+  "net/http"
+  "os/signal"
+  "syscall"
+
+  "github.com/gin-gonic/autotls"
+  "github.com/gin-gonic/gin"
+)
+
+func main() {
+  // Create context that listens for the interrupt signal from the OS.
+  ctx, stop := signal.NotifyContext(
+    context.Background(),
+    syscall.SIGINT,
+    syscall.SIGTERM,
+  )
+  defer stop()
+
+  r := gin.Default()
+
+  // Ping handler
+  r.GET("/ping", func(c *gin.Context) {
+    c.String(http.StatusOK, "pong")
+  })
+
+  log.Fatal(autotls.RunWithContext(ctx, r, "example1.com", "example2.com"))
+}
+```

_example/example3/main.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"context"
+	"log"
+	"net/http"
+	"os/signal"
+	"syscall"
+
+	"github.com/gin-gonic/autotls"
+	"github.com/gin-gonic/gin"
+)
+
+func main() {
+	// Create context that listens for the interrupt signal from the OS.
+	ctx, stop := signal.NotifyContext(
+		context.Background(),
+		syscall.SIGINT,
+		syscall.SIGTERM,
+	)
+	defer stop()
+
+	r := gin.Default()
+
+	// Ping handler
+	r.GET("/ping", func(c *gin.Context) {
+		c.String(http.StatusOK, "pong")
+	})
+
+	log.Fatal(autotls.RunWithContext(ctx, r, "example1.com", "example2.com"))
+}