Add link to phi0 generator

src/phi0.c

@@ -3,7 +3,8 @@
 //
 // An approximation of the function
 //
-// This file is generated by the gen_phi0 scritps
+// This file is generated by the gen_phi0 script, from codec2
+// https://github.com/drowe67/codec2/blob/master/script/gen_phi0
 // Any changes should be made to that file, not this one
 
 #include <stdint.h>