Fixes unclear sentence in finder.rst

[kane-menicou]

No description provided.

[OskarStark]

Much better, thank you

[javiereguiluz]

I agree that the original phrase can be improved ... but I'm not sure about the new proposal because it still doesn't explain the methods explicitly (it says "granular results" instead of "files only or dirs only").

What about something like this instead:

By default, the Finder returns both files and directories. If you need to find
either files or directories only, use the :method:`Symfony\\Component\\Finder\\Finder::files`
and :method:`Symfony\\Component\\Finder\\Finder::directories` methods::

[javiereguiluz]

@kane-menicou thanks for improving Symfony Docs and thanks for being so open to our comments!