[Docs] Add example for building Personal AI Assistant using Mem0 (#1486)

docs/examples/customer-support-agent.mdx

@@ -24,6 +24,9 @@ Below is the simplified code to create and interact with a Customer Support AI A
 from openai import OpenAI
 from mem0 import Memory
 
+# Set the OpenAI API key
+os.environ['OPENAI_API_KEY'] = 'sk-xxx'
+
 class CustomerSupportAIAgent:
     def __init__(self):
         """