docs: Adding an example for AddRemoteFile and DeleteFile (#1303)

examples/files_remote/files_remote.go

@@ -0,0 +1,30 @@
+package main
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/slack-go/slack"
+)
+
+func main() {
+	api := slack.New("YOUR_TOKEN")
+	params := slack.RemoteFileParameters{
+		Title:       "My File",
+		ExternalID:  "my-file-123",
+		ExternalURL: "https://raw.githubusercontent.com/slack-go/slack/master/README.md",
+	}
+	file, err := api.AddRemoteFileContext(context.Background(), params)
+	if err != nil {
+		fmt.Printf("%s\n", err)
+		return
+	}
+	fmt.Printf("Name: %s, URL: %s\n", file.Name, file.URLPrivate)
+
+	err = api.DeleteFileContext(context.Background(), file.ID)
+	if err != nil {
+		fmt.Printf("%s\n", err)
+		return
+	}
+	fmt.Printf("File %s deleted successfully.\n", file.Name)
+}