selftests: Add information about TAP conformance in tests

Although "TAP" word is being used already in documentation, but it hasn't
been defined in informative way for developers that how to write TAP
conformant tests and what are the benefits. Write a short brief about it.
Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Documentation/dev-tools/kselftest.rst

@@ -228,6 +228,13 @@ In general, the rules for selftests are
  * Don't cause the top-level "make run_tests" to fail if your feature is
    unconfigured.
 
+ * The output of tests must conform to the TAP standard to ensure high
+   testing quality and to capture failures/errors with specific details.
+   The kselftest.h and kselftest_harness.h headers provide wrappers for
+   outputting test results. These wrappers should be used for pass,
+   fail, exit, and skip messages. CI systems can easily parse TAP output
+   messages to detect test results.
+
 Contributing new tests (details)
 ================================