Documentation: KUnit: Rework writing page to focus on writing tests

We now have dedicated pages on running tests. Therefore refocus the
usage page on writing tests and add content from tips page and
information on other architectures.
Signed-off-by: Harinder Singh <sharinder@google.com>
Reviewed-by: Tim Bird <tim.bird@sony.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Link: https://lore.kernel.org/r/20211217044911.798817-6-sharinder@google.comSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/dev-tools/kunit/index.rst

@@ -102,7 +102,7 @@ How do I use it?
 *   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 - KUnit features.
+*   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

Documentation/dev-tools/kunit/start.rst

@@ -243,7 +243,7 @@ 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 - KUnit features.
+*   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