Add an outlined version of logo.png and icon.png and put it in README.md

Author: Lorenzo Cerqua

README.md

@@ -2,7 +2,7 @@
 
 <p align="center">
   <a href="https://godotengine.org">
-    <img src="logo.svg" width="400" alt="Godot Engine logo">
+    <img src="logo_outlined.svg" width="400" alt="Godot Engine logo">
   </a>
 </p>