Add Andy Potter to CREDITS

Again, this is inferred from their Gerrit username. I've also emailed
them to confirm the name.

Change-Id: I2aced94a5a0a8847c86da0e425db4130b4dccb69
diff --git a/docs/CREDITS b/docs/CREDITS
index eaaad5b..018ac9e 100644
--- a/docs/CREDITS
+++ b/docs/CREDITS
@@ -678,6 +678,7 @@
 Christian Soffke
 Juan Gonzalez
 Yangyong Wu
+Andy Potter
 
 The libmad team
 The wavpack team