Update README.md

Co-authored-by: Andrew Kiss <[email protected]>

README.md

@@ -192,8 +192,9 @@ Converts `test_topo.png` to `test_topo.nc` for use as a test input file for `top
 ## editTopo.py
 
 `editTopo.py` provides a GUI for hand-editing `topog.nc` files, recording every
-change, and applying these changes to other files. This is an updated version of
-Alistair Adcroft's `editTopo.py` from
+change, and applying these changes to other files. This was initially copied from 
+[here](https://github.com/COSIMA/topogtools/blob/6b4983127aa18dfdf1b62b2e18b581d82d4a64d4/editTopo.py),
+which is in turn an updated version of Alistair Adcroft's `editTopo.py` from
 [here](https://github.com/aekiss/MOM6-examples/blob/1c3dc5216139f84b20ce3a5d8ea758bdc7912e8e/ice_ocean_SIS2/OM4_025/preprocessing/editTopo.py)
 and is under a [LGPLv3
 license](https://github.com/NOAA-GFDL/MOM6-examples/blob/dev/gfdl/LICENSE.md).