Let base example fail if file my_key is missing

Co-authored-by: Andrei Politov <andrei.politov@tu-dresden.de>

base/main.py

@@ -2,8 +2,13 @@
 # Find instructions how to install dependencies and how to run this script in README.md
 from openai import OpenAI
 my_api_key = ""
-with open("my_key") as keyfile:
-    my_api_key = keyfile.readline()[:-1]
+try:
+    with open("my_key") as keyfile:
+        my_api_key = keyfile.readline().strip()
+except FileNotFoundError:
+    print("Error: The file 'my_key' was not found. Please make sure the file exists and contains your API key.")
+    exit(1)
+
 
 client = OpenAI(base_url="https://llm.scads.ai/v1",api_key=my_api_key)
 # Get models