Removed outdated section about filesystem handling

Filesystem adapters are now handled by the Listen gem.

Therefore I propose to delete this entire section, since this is all handled transparently. I have created a Wiki page and moved the content there. https://github.com/guard/guard/wiki/Efficient-Filesystem-Handling
Merge pull request #438 from tilsammans/patch-1

Removed outdated section about filesystem handling [ci skip]