Create Build chat-based apps.md

Author: codehariom

Build chat-based apps.md

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+This code involves using Streamlit to create a chat interface:
+
+    with st.chat_message("user"):
+creates a chat message container with the user's name displayed as "user".
+
+    st.write("Hello 👋")
+     
+writes a greeting message.
+    
+    st.line_chart(np.random.randn(30, 3))
+displays a line chart with random data.
+
+    st.chat_input("Say something")
+displays a chat input widget where the user can type a message.