added readme

test/readme.txt

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+This directory contains test code for automatic regression testing of the CC65
+compiler.
+
+
+/val  - the bulk of tests are contained here, individual tests should exit with
+        an exit code of EXIT_SUCCESS when they pass, or EXIT_FAILURE on error
+
+/ref  - these tests produce output that must be compared with reference output
+
+/err  - contains tests that MUST NOT compile
+
+/misc - a few tests that need special care of some sort
+
+
+to run the tests use "make clean all" in this (top) directory, the makefile
+should exit with no error.