doc: Kronos documentation improvements based on editorial review

    This commit improves the documentation with following updates:
     - Split up large sentences.
     - Simplify and commonize vocabulary.
     - Use present tense.
     - Use the active voice.
     - Refer to "you" rather than "the user".
     - Remove any ambiguity in instructions.
     - Use sentence case for headings.
     - Heading/paragraph before the code snippet is ends with ":".

Signed-off-by: Archish Venkatesh <archish.venkatesh@arm.com>