bpo-38558: Link to further docs from walrus operator mention in tutorial (GH-16973)

diff --git a/Doc/faq/design.rst b/Doc/faq/design.rst
index 75cd20f..df3dbf4 100644
--- a/Doc/faq/design.rst
+++ b/Doc/faq/design.rst
@@ -148,6 +148,8 @@
 to tell Python which namespace to use.
 
 
+.. _why-can-t-i-use-an-assignment-in-an-expression:
+
 Why can't I use an assignment in an expression?
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