add note about building/running test programs

README.txt

@@ -29,9 +29,13 @@ machines.
 
 3 - Build codes-base
 
-    make clean && make && make install
+    make clean && make && make install && make tests
 
-4 - codes-base uses flex and bison (or lex and yacc) to generate several parsers.
+4 - (optional) run test programs
+
+    make check
+
+5 - codes-base uses flex and bison (or lex and yacc) to generate several parsers.
 These tools auto-generate C source files. To remove all of the autogenerated
 files for these parsers, execute