docs: Tweak Getting Started Guide
docs: Tweak Getting Started Guide

This commit makes a number of small changes to the Getting Started Guide
to address feedback from user studies on 9/21.

quilt/quilt,kklin/quilt,ejj/quilt-dev,quilt/quilt,NetSys/quilt,kelda/kelda,kklin/kelda,LuiseV/quilt,kklin/kelda,quilt/quilt,ejj/quilt-dev,LuiseV/quilt,LuiseV/quilt,kklin/kelda,LuiseV/quilt,LuiseV/quilt,kklin/kelda,NetSys/quilt,NetSys/quilt,ejj/quilt-dev,kklin/quilt,kelda/kelda,quilt/quilt,NetSys/quilt,kelda/kelda,kklin/quilt,ejj/quilt-dev,kklin/quilt,kelda/kelda,NetSys/quilt