Created folders in vendors

Added so users should not make 2 cakephp folders themselves(I didn't understand it at first) if they are following instructions from here:http://book.cakephp.org/3.0/en/installation.html#installing-with-git-github
Minor grammar fixes
Added new section

I added a little modified new section, Keeping up to date with the latest CakePHP changes, from 3.0 documentation(http://book.cakephp.org/3.0/en/installation.html#installing-with-git-github).
Deleted empty file in vendors
Merge pull request #22 from Aleksa-Savic/master

Readme improvements.