[MINOR] Add information about the test suites in the INSTALL file.

INSTALL

@@ -139,6 +139,13 @@ You need a GNU Make (or equivalent). The Makefile defines the following goals:
   installs binaries into $(BINDIR), manpages into $(MANDIR)/man1,
   and registers the cduce_lib library with findlib.
 
+- make test
+  runs the first test suite, all the tests in this suite should pass.
+
+- make extendedtest
+  runs the extended test suite, some tests are broken and need investigation,
+  others are testing future features of CDuce.
+
 - make clean
   back to the starting point
 
@@ -201,7 +208,3 @@ which cduce
 
 The directory tests contains few tests to check if the ocaml interface was 
 compiled correctly. 
-
-cd tests/ocaml
-make
-