Clean up README

While style argueably is a mostly a matter of taste, this change aims to

  * make it easier to jump to searched paragraphs by consolidating
    heading levels
  * group similar information together
  * make copy and paste of command line examples easier
Clean up README

While style argueably is a mostly a matter of taste, this change aims to

  * make it easier to jump to searched paragraphs by consolidating
    heading levels
  * group similar information together
  * make copy and paste of command line examples easier