Regenerate CliTest.wrongAbiVersion test, add readme

compiler/testData/cli/wrongAbiVersionLib/ClassWithWrongAbiVersion.kt.txt

@@ -0,0 +1,13 @@
+/*
+To regenerate this test:
+  1. Change JvmAbi.VERSION to -1
+  2. Run 'ant dist'
+  3. Rename this file and wrong-package: delete 'txt' extension
+  4. Compile two files with the newly built compiler from dist/
+  5. Rename files back: add 'txt' extension
+  6. Change JvmAbi.VERSION back to its old value
+  7. Run 'ant dist'
+After these steps, the test should succeed
+*/
+
+class ClassWithWrongAbiVersion

compiler/testData/cli/wrongAbiVersionLib/wrong-class-source

@@ -1 +0,0 @@
-class ClassWithWrongAbiVersion