Add architecture diagram

Author: vinhnx

README.md

@@ -39,6 +39,16 @@ Clendar - Minimal Calendar
 
 > [Landing Page](http://vinhnx.github.io/clendar-site)
 
+### Architecture
+
+<p align="center">
+  <img src="./clendar_diagram.png" alt="diagram" />
+</p>
+
+<p align="center">
+  <em>* Diagram generated by <a href="https://github.com/ahmedkhaleel2004/gitdiagram">gitdiagram</em>
+</p>
+
 ### Table of Contents
 
 - 📋 [About](#about)