Update filesystem.rst

Author: flip111

components/filesystem.rst

@@ -68,6 +68,13 @@ On POSIX filesystems, directories are created with a default mode value
 
  This function ignores already existing directories.
 
+.. note::
+
+ The directory permissions are affected by the current `umask`_.
+ Set the umask for your webserver, use PHP's :phpfunction:`umask`
+ function or use the :phpfunction:`chmod` function after the
+ directory has been created.
+
 exists
 ~~~~~~
 
@@ -278,3 +285,4 @@ Learn More
  filesystem/*
 
 .. _`Packagist`: https://packagist.org/packages/symfony/filesystem
+.. _`umask`: https://en.wikipedia.org/wiki/Umask