Update README.md

[mokevnin]

It looks like the index.php is inside the public directory, but there is no information about it.

[coveralls]

Coverage remained the same at ?% when pulling 9a1c775 on mokevnin:patch-1 into 4d490ab on slimphp:4.x.

[froschdesign]

It looks like the index.php is inside the public directory, but there is no information about it.

Good catch, but the vendor directory does not belong in the public area. My suggestion: add a filename before the code example or as commend in the code example.

[mokevnin]

One more time)