Add release note for EL7 client repository removal

Foreman 3.14 drops EL7 builds for the client repositories.

Link: https://community.theforeman.org/t/drop-el7-packages-from-foreman-client-with-foreman-3-14/40505

guides/doc-Release_Notes/topics/foreman.adoc

@@ -11,7 +11,14 @@ There are no highlights with Foreman {ProjectVersion}.
 
 // If this section would be empty otherwise, uncomment the following line:
 ifndef::foreman-deb[]
-There are no upgrade warnings with Foreman {ProjectVersion}.
+=== EL 7 client repositories dropped
+
+RHEL 7 is out of maintenance since June 2024 and at the same time CentOS Linux 7 went end of life.
+With Foreman 3.14, the client repository is no longer built for EL 7.
+This primarily affects Katello and OpenSCAP users.
+
+For more details, see the https://community.theforeman.org/t/drop-el7-packages-from-foreman-client-with-foreman-3-14/40505[removal RFC].
+
 endif::[]
 ifdef::foreman-deb[]
 === Running Foreman on Debian 11 (Bullseye) is not supported anymore