Clean up the README
Clean up the README

Fix a few typos and reformat the build instructions.
evenator/marti_common,swri-robotics/marti_common,evenator/marti_common,evenator/marti_common,swri-robotics/marti_common,elliotjo/marti_common,swri-robotics/marti_common,evenator/marti_common,elliotjo/marti_common,elliotjo/marti_common,elliotjo/marti_common,swri-robotics/marti_common