[master] 6daaa5948 give advise on how to override the submodule url

[Nils Goroll]

commit 6daaa5948fa6ef5913345ed9ae923ec7514c7a1a
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Tue May 27 09:54:53 2025 +0200

    give advise on how to override the submodule url

diff --git a/doc/sphinx/installation/install_source.rst b/doc/sphinx/installation/install_source.rst
index 071600d0a..20cf3ba85 100644
--- a/doc/sphinx/installation/install_source.rst
+++ b/doc/sphinx/installation/install_source.rst
@@ -21,7 +21,13 @@ https://varnish-cache.org/releases/ .
 Alternatively, if you want to hack on Varnish, you should clone our
 git repository by doing.
 
-      ``git clone https://github.com/varnishcache/varnish-cache``
+      ``git clone -r https://github.com/varnishcache/varnish-cache``
+
+This will recursively check out the vtest2 sources from the default repository
+URL. If you prefer to use vtest2 from a non-default (local) repository, you can
+tell git to replace the url:
+
+        ``git config url.$YOUR_VTEST2_URL.insteadOf https://github.com/vtest/VTest2.git``
 
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 -----------------------------