Clarify ambigious check wrt return codes

README.md

@@ -44,9 +44,7 @@ _The checking of items on this list is still being developed. Checked items shou
   * [x] `sha2.c`
   * [ ] `aes.c`
   * [x] `randombytes.c`
-* [ ] API functions return `0` on success, negative on failure
-    * [x] 0 on success
-    * [ ] Negative on failure (within restrictions of FO transform).
+* [x] API functions return `0` on success
 * [x] No dynamic memory allocations
 * [ ] No branching on secret data (dynamically checked using valgrind)
 * [ ] No access to secret memory locations (dynamically checked using valgrind)