Polling fallback message help

Motivated by: #284. [ci skip]
Now that we have WIKI pages for Mac/Windows, I was thinking that I would drop the "potential fixes" section (and Bundler/Sass example) and just say this:

> 1. ...
> 1. Using [Sass](http://sass-lang.com/) which includes an ancient (the “dinosaur” type of ancient) version of the Listen gem.

> Please visit the [installation section of the Listen WIKI](https://github.com/guard/listen/wiki#installation) for information on potential fixes.

It seems like the first three bullet points have been solidified. If we move everything else I've proposed adding into the WIKI, then it will make it easy for all of us to make edits.

At this point, should I update my PR and we can discuss from there?