Update README.md

ISSOtm link

Author: dmitry-shechtman

README.md

@@ -29,7 +29,7 @@ All the differences from the animated GIF (that we're aware of):
 ## Thanks
 
 * [calc84maniac](https://github.com/calc84maniac/) for some mad optimisations
-* [ISSOtm](https://github.com/ISSOtm) for saner optimisations
+* [ISSOtm](https://codeberg.org/ISSOtm) for saner optimisations
 
 ## Licenses