README.

README.md

@@ -66,8 +66,14 @@ To retrieve and compile the source code, type:
   make
 ```
 
-To test the library using `afl-fuzz`, type:
+To set up an `opam` switch that allows testing Sek, type this (only once):
 ```
-    make test
-    # This command runs forever; interrupt it with Ctrl+C when you wish
+  make -C fuzz setup
+```
+You must also install [AFL](https://github.com/google/AFL).
+
+Then, to test the library using `afl-fuzz`, type:
+```
+  make test
+  # This command runs forever; interrupt it with Ctrl+C when you wish
 ```