Update README.md

Author: wdduncan

README.md

@@ -8,6 +8,9 @@ Other ontologies are also reviewed.
 
 More information can be found at http://obofoundry.org/ontology/pain
 
+## Term Spreadsheet
+[Google spreadsheet for adding terms.](https://docs.google.com/spreadsheets/d/1sVXeL8tnsFrqt8x9v4T9Euka-L5_y4RSvrlPgArfp8U/edit#gid=0)  
+
 ## Versions
 
 ### Stable release versions
@@ -28,4 +31,4 @@ Please use this GitHub repository's [Issue tracker](https://github.com/wdduncan/
 
 ## Acknowledgements
 
-This ontology repository was created using the [Ontology Development Kit (ODK)](https://github.com/INCATools/ontology-development-kit).
+This ontology repository was created using the [Ontology Development Kit (ODK)](https://github.com/INCATools/ontology-development-kit).