minor #7670 document that FileSystem.mkdir works recursively (SimonHeimberg)

This PR was submitted for the 3.2 branch but it was merged into the 2.7 branch instead (closes #7670).

Discussion
----------

document that FileSystem.mkdir works recursively

This is documented on the api of this method.

Commits
-------

9e228d0 write that FileSystem.mkdir works recursively

Author: xabbuh

components/filesystem.rst

@@ -53,7 +53,7 @@ endpoint for filesystem operations::
 mkdir
 ~~~~~
 
-:method:`Symfony\\Component\\Filesystem\\Filesystem::mkdir` creates a directory.
+:method:`Symfony\\Component\\Filesystem\\Filesystem::mkdir` creates a directory recursively.
 On POSIX filesystems, directories are created with a default mode value
 `0777`. You can use the second argument to set your own mode::