Add custom port env

Signed-off-by: Odyssey <odyssey346@disroot.org>

main.go

@@ -3,6 +3,8 @@ package main
 import (
 	"log"
 
+	"os"
+
 	"github.com/gofiber/fiber/v2"
 
 	"github.com/gofiber/template/html"
@@ -112,5 +114,11 @@ func main() {
 		c.Response().Header.Del(fiber.HeaderServer)
 		return nil
 	})
-	log.Fatal(app.Listen(":3000"))
+	val, ok := os.LookupEnv("GOTHUB_PORT")
+	if !ok {
+		val = "3000"
+	} else {
+		log.Println("Using port from env variable")
+	}
+	log.Fatal(app.Listen(":" + val))
 }