Make the titles in TOC just a tad cleaner

for the TOC headings, how do you feel about removing "with CodeRabbit"?

So  _Get Started with CodeRabbit_ becomes _Get Started_

Add _CodeRabbit to your repository_ becomes _Add to your repository_

All of this is with the assumption the user will know we are referring to CodeRabbit by virtue of where they are. 

My reasoning: simplify, make the TOC easier to scan.