Add proper readmes

test/asm/listing/readme.txt

@@ -0,0 +1,27 @@
+Overall test:
+-------------
+
+These testcases can be used to test different aspects of the assembler.
+The name of a test is everything in the form <test>.s.
+
+The following reference files can be added:
+
+- <test>.bin-ref:
+  This is a reference for the resulting binary.
+  The binary as binary tested against this file.
+  If they are not equal, the test fails.
+
+- <test>.list-ref
+  This is a reference for the resulting listing output
+  This file *must* have the first line of the listing removed, as that
+  contains a ca65 version string, and almost always this will be changed!
+
+
+Note that the resulting .bin file is generated twice: Once with no listing
+file, and once with listing file. This way, one can find out if the listing
+file generation changes anything with the resulting binary output.
+
+
+TODO:
+- add the possibility to test for specific error output that are to be
+  expected