Add architecture diagram

Architecture.md

@@ -1,6 +1,36 @@
 # Architecture
 
+## Introduction
+
+To get the PDP-10 to solve sudokus and learn how to code in PDP-10 assembly, we
+should first consider, what functions we need, and how to structure the code, so
+we can build small, fast and reusable functions. Since organising code in
+assembly is a lot harder than in high-level programming languages such as LISP
+and C, we should first plan how the program should look like, before we start
+writing the actual code. This way, we can encapsulate the code and make it
+reusable. The program will follow a simple flow:
+
 ```mermaid
-flowchart LR
-    id
+---
+title: Program-Flow
+---
+flowchart TD
+    start((Start))
+    print1["Print Welcome Message"]
+    cmdline["Read file name from command line"]
+    fileexists{"File Exists?"}
+    loadfile["Load grid from file"]
+    print2["Print board"]
+    solve[["Solve the puzzle"]]
+    print3["Print solved board"]    
+    stop((Stop))
+
+    start --> print1
+    print1 --> fileexists
+    fileexists -->|No| stop
+    fileexists -->|Yes| loadfile
+    loadfile --> print2
+    print2 --> solve
+    solve --> print3
+    print3 --> stop
 ```