improve docs (+ sign-off)

This replaces PR #24, in response to the sign-off request by @rxaviers. I previously deleted my fork and as far as I can tell GitHub doesn't allow you to push additional commits to a PR after the fork is deleted, even if you create a new fork.

I made a number of minor changes to improve the readme:

 * "i18n" should be lowercase
 * "software" is already plural so no need to add an "s"
 * comma should only be used before "and" with a list of items greater than two:
   "foo, bar, and baz" but "foo and bar"
 * "both foo or bar" should either by "both foo and bar" or "either foo or bar",
   so I used the former
 * "Node.js" should be titlecase
 * "Attention" typo
 * pronoun "its" should be "their" b/c the subject is plural "libraries"
 * changed "some" to "several" b/c it sounds more natural

Signed-off-by: Nick Patch <patch@cpan.org>