minor #19423 [Routing] [url generation] note on forcing https (dbu)

This PR was submitted for the 7.1 branch but it was merged into the 6.3 branch instead.

Discussion
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[Routing] [url generation] note on forcing https

this got me confused when trying to ignore the problem i had in #19422 - i think cross-linking the proxy configuration here is helpful for people who also try to skirt doing a correct setup in their infrastructure.

Commits
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dc2fbdb note on forcing https

Author: javiereguiluz

routing.rst

@@ -2492,6 +2492,15 @@ when the route doesn't exist::
 Forcing HTTPS on Generated URLs
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
+.. note::
+
+    If your server runs behind a proxy that terminates SSL, make sure to
+    :doc:`configure Symfony to work behind a proxy </deployment/proxies>`
+
+    The configuration for the scheme is only used for non-HTTP requests.
+    The ``schemes`` option together with incorrect proxy configuration will
+    lead to a redirect loop.
+
 By default, generated URLs use the same HTTP scheme as the current request.
 In console commands, where there is no HTTP request, URLs use ``http`` by
 default. You can change this per command (via the router's ``getContext()``