Link to provis as a source for the attention visualization

hexviz/app.py

@@ -58,5 +58,5 @@ showmol(xyzview, height=500, width=800)
 st.markdown(f'PDB: [{pdb_id}](https://www.rcsb.org/structure/{pdb_id})', unsafe_allow_html=True)
 
 """
-More models will be added soon.
+More models will be added soon. The attention visualization is inspired by [provis](https://github.com/salesforce/provis#provis-attention-visualizer).
 """