Update app.py

app.py

@@ -85,6 +85,8 @@ demo = gr.Blocks()
 
 with demo:
     gr.Markdown("# PDB viewer using 3Dmol.js")
+    gr.Markdown("""If using please cite:
+    > 3Dmol.js: molecular visualization with WebGL, Nicholas Rego, David Koes , Bioinformatics, Volume 31, Issue 8, April 2015, Pages 1322–1324, https://doi.org/10.1093/bioinformatics/btu829""")
     with gr.Row():
         with gr.Box():
             inp = gr.Textbox(