Link to process document in Future API standard evolution section

Author: rgommers

spec/future_API_evolution.md

@@ -3,10 +3,7 @@
 ## Scope extensions
 
 Proposals for scope extensions in a future version of the API standard will follow
-the process documented at:
-
-TODO: link to specific document in https://github.com/data-apis/governance once
-it is available.
+the process documented at https://github.com/data-apis/governance/blob/master/process_document.md
 
 In summary, proposed new APIs go through several maturity stages, and will only be
 accepted in a future version of this API standard once they have reached the "Final"