Add a few comments

app.py

@@ -13,24 +13,27 @@
 import google.generativeai as genai
 
 # WARNING: Do not share code with you API key hard coded in it.
+# Get your Gemini API key from: https://aistudio.google.com/app/apikey
 GOOGLE_API_KEY=""
 genai.configure(api_key=GOOGLE_API_KEY)
 
 # The rate limits are low on this model, so you might need to switch to `gemini-pro`
 model = genai.GenerativeModel('gemini-1.5-pro-latest')
 
 app = Flask(__name__)
-ALLOWED_EXTENSIONS = {"txt", "pdf", "png", "jpg", "jpeg", "gif", "csv"}
+ALLOWED_EXTENSIONS = {"png", "jpg", "jpeg"}
 
 chat_session = model.start_chat(history=[])
 next_message = ""
 next_image = ""
 
 def allowed_file(filename):
+    """Returns if a filename is supported via its extension"""
     return "." in filename and filename.rsplit(".", 1)[1].lower() in ALLOWED_EXTENSIONS
 
 @app.route("/upload", methods=["POST"])
 def upload_file():
+    """Takes in a file, checks if it is valid, and saves it for the next request to the API"""
     global next_image
 
     if "file" not in request.files:
@@ -57,10 +60,12 @@ def upload_file():
 
 @app.route("/", methods=["GET"])
 def index():
+    """Renders the main homepage for the app"""
     return render_template("index.html", chat_history=chat_session.history)
 
 @app.route("/chat", methods=["POST"])
 def chat():
+    """Takes in the message the user wants to send to the Gemini API, saves it"""
     global next_message
     next_message = request.json["message"]
     print(chat_session.history)
@@ -69,12 +74,14 @@ def chat():
 
 @app.route("/stream", methods=["GET"])
 def stream():
+    """Streams the response from the serve for both multi-modal and plain text requests"""
     def generate():
         global next_message
         global next_image
         assistant_response_content = ""
 
         if next_image != "":
+            # This only works with `gemini-1.5-pro-latest`
             response = chat_session.send_message([next_message, next_image], stream=True)
             next_image = ""
         else: