add changelog

Author: ab9rf

docs/changelog.txt

@@ -62,6 +62,7 @@ Template for new versions:
 - `sort`: Using the squad unit selector will no longer cause Dwarf Fortress to crash on exit
 
 ## Misc Improvements
+-- The ``fpause`` console command can now be used to force world generation to pause (as it did prior to version 50).
 
 ## Documentation