Add README.md portrait (#16)

* Add portrait image

* Add portrait image to README.md

Author: Kitt3120

.github/assets/portrait.png

@@ -1,3 +1,7 @@
+<p align="center">
+  <img src="https://raw.githubusercontent.com/Kitt3120/lum/main/.github/assets/portrait.png" width="512">
+</p>
+
 # lum
 
 Lum Discord Bot