Document $suffix argument to tempnam()

Author: jdufresne

components/filesystem.rst

@@ -286,6 +286,12 @@ exception on failure::
 
     // returns a path like : /tmp/prefix_wyjgtF
     $filesystem->tempnam('/tmp', 'prefix_');
+    // returns a path like : /tmp/prefix_wyjgtF.png
+    $filesystem->tempnam('/tmp', 'prefix_', '.png');
+
+.. versionadded:: 4.4
+
+    The option to set a suffix in  ``tempnam()`` was introduced in Symfony 4.4.
 
 ``dumpFile``
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