Remove unnecessary words and organize content in keras.md

[stumblefiend]

Improvements to the clarity and structure of the documentation. Metrics include:

• 30% fewer words.
• The tone shifts more neutral by 9%
• No significant difference in Flesch-Kincaid readability scores.

[stumblefiend]

Thanks for the advice @mihaimaruseac ! I have bookmarked that commit message resource and updated the subject of the pull request.

[stumblefiend]

Is there anything I need to do to make progress toward either getting this pull request approved or denied?