Documentation: Kunit: Update architecture.rst for minor fixes

Updated the architecture.rst page with the following changes:
-Add missing article _the_ across the document.
-Reword content across for style and standard.
-Update all occurrences of Command Line to Command-line
 across the document.
-Correct grammatical issues, for example,
 added _it_wherever missing.
-Update all occurrences of “via" to either use
 “through” or “using”.
-Update the text preceding the external links and pushed the full
 link to a new line for better readability.
-Reword content under the config command to make it more clear and concise.

Signed-off-by: Sadiya Kazi <sadiyakazi@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>