Documentation: kunit: Fix "How Do I Use This" / "Next Steps" sections

The "How Do I Use This" section of index.rst and "Next Steps" section of
start.rst were just copies of the table of contents, and therefore
weren't really useful either when looking a sphinx generated output
(which already had the TOC visible) or when reading the source (where
it's just a list of files that ls could give you).

Instead, provide a small number of concrete next steps, and a bit more
description about what the pages contain.

This also removes the broken reference to 'tips.rst', which was
previously removed.

Fixed git am whitespace complaints during commit:
Shuah Khan <[e-mail]>

Fixes: 4399c737a97d ("Documentation: kunit: Remove redundant 'tips.rst' page")
Signed-off-by: David Gow <[e-mail]>
Reviewed-by: Sadiya Kazi <[e-mail]>
Reviewed-by: Bagas Sanjaya <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

Documentation/dev-tools/kunit/index.rst

···
 How do I use it?
 ================
 
-*   Documentation/dev-tools/kunit/start.rst - for KUnit new users.
-*   Documentation/dev-tools/kunit/architecture.rst - KUnit architecture.
-*   Documentation/dev-tools/kunit/run_wrapper.rst - run kunit_tool.
-*   Documentation/dev-tools/kunit/run_manual.rst - run tests without kunit_tool.
-*   Documentation/dev-tools/kunit/usage.rst - write tests.
-*   Documentation/dev-tools/kunit/tips.rst - best practices with
-    examples.
-*   Documentation/dev-tools/kunit/api/index.rst - KUnit APIs
-    used for testing.
-*   Documentation/dev-tools/kunit/faq.rst - KUnit common questions and
-    answers.
+You can find a step-by-step guide to writing and running KUnit tests in
+Documentation/dev-tools/kunit/start.rst
+
+Alternatively, feel free to look through the rest of the KUnit documentation,
+or to experiment with tools/testing/kunit/kunit.py and the example test under
+lib/kunit/kunit-example-test.c
+
+Happy testing!

Documentation/dev-tools/kunit/start.rst

···
 Next Steps
 ==========
 
-*   Documentation/dev-tools/kunit/architecture.rst - KUnit architecture.
-*   Documentation/dev-tools/kunit/run_wrapper.rst - run kunit_tool.
-*   Documentation/dev-tools/kunit/run_manual.rst - run tests without kunit_tool.
-*   Documentation/dev-tools/kunit/usage.rst - write tests.
-*   Documentation/dev-tools/kunit/tips.rst - best practices with
-    examples.
-*   Documentation/dev-tools/kunit/api/index.rst - KUnit APIs
-    used for testing.
-*   Documentation/dev-tools/kunit/faq.rst - KUnit common questions and
-    answers.
+If you're interested in using some of the more advanced features of kunit.py,
+take a look at Documentation/dev-tools/kunit/run_wrapper.rst
+
+If you'd like to run tests without using kunit.py, check out
+Documentation/dev-tools/kunit/run_manual.rst
+
+For more information on writing KUnit tests (including some common techniques
+for testing different things), see Documentation/dev-tools/kunit/usage.rst