Update README information and formatting.

- update the "Requirements" section to list the gems that gi_cat_driver
  depends on

- update "Installation" to note that required gems can be installed with
  bundler

- update link to annotated source code documentation (github
  automatically redirected the old link, still better to use the
  correct link)

- remove an extra character from the "Releasing" section

- wrap lines at 80 columns for better source readability (rendering of
  the markdown is unchanged)

- use triple-backticks for code blocks rather than indentation