minor #17120 [Filesystem] Add more information about dumpFile (mohamedGasmii)

This PR was squashed before being merged into the 6.0 branch.

Discussion
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[Filesystem] Add more information about dumpFile

Add more information about dumpFile :
 1- creating file if it does not exists.
 2- mention that the old data inside the file will be lost if it exists.

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Commits
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37106b4 [Filesystem] Add more information about dumpFile

Author: javiereguiluz

components/filesystem.rst

@@ -302,6 +302,12 @@ complete new file (but never a partially-written file)::
 
 The ``file.txt`` file contains ``Hello World`` now.
 
+If either the file or its containing directory doesn't exist, this method
+creates them.
+
+After writing the temporary file, this method use :method:`Symfony\\Component\\Filesystem\\Filesystem::rename`
+and set the third argument to true, so if the file exists, it will be overridden and the old content inside will be lost.
+
 ``appendToFile``
 ~~~~~~~~~~~~~~~~