add route for robots.txt.

app/app.py

@@ -12,5 +12,10 @@ app.add_api("swagger.yml")
 def home ():
     return render_template("home.html")
 
+@app.route("/robots.txt")
+@app.route("/robots")
+def robots():
+    return render_template("robots.txt")
+
 if __name__ == "__main__":
     app.run(host="0.0.0.0", debug=True)