Add myself to authors

Since I intend to stick around & be an active maintainer, add me to the list of authors in the README and in the gemspec for future gem releases:

~~~ sh
╭─{ yaauie @ beorn in ~/src/redis-rb (✔ add-me-to-authors) }
╰─● git shortlog -sn | grep Biesemeyer
    23	Ryan Biesemeyer
[success.]
~~~