minor #6336 Added minor clarification (ThomasLandauer)

This PR was submitted for the 2.8 branch but it was merged into the 2.3 branch instead (closes #6336).

Discussion
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Added minor clarification

It was not clear if the following code applies to BinaryFileResponse only or to all file responses.

Since the following two paragraphs ("It is possible to delete ..." and "If you just created...") also apply to BinaryFileResponse only, it would be even better to have a separate heading for BinaryFileResponse, but I don't know how to create another sub-heading at this level.

Commits
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9490b08 Added minor clarification

Author: weaverryan

components/http_foundation/introduction.rst

@@ -474,7 +474,8 @@ if it should::
 
     BinaryFileResponse::trustXSendfileTypeHeader();
 
-You can still set the ``Content-Type`` of the sent file, or change its ``Content-Disposition``::
+With the ``BinaryFileResponse``, you can still set the ``Content-Type`` of the sent file,
+or change its ``Content-Disposition``::
 
     $response->headers->set('Content-Type', 'text/plain');
     $response->setContentDisposition(