add simple README for wcat tests

initial-utilities/wcat/README.md

@@ -0,0 +1,19 @@
+
+In this directory, you should write the program `wcat.c` and compile it into
+the binary `wcat'.
+
+After doing so, you can run the tests from this directory by running the
+`run-tests.sh` script. If all goes well, you will see:
+
+```sh
+prompt> ../../tester/run-tests.sh
+test 1: passed
+test 2: passed
+test 3: passed
+test 4: passed
+test 5: passed
+test 6: passed
+test 7: passed
+prompt>
+```
+