Add link to S6023

rules/S7172/cfamily/rule.adoc

@@ -90,7 +90,7 @@ void perform(Node node, optional<bool> recursive, Action action) {
 }
 ----
 
-In this simple case, the use of both `recursive` and `++*recursive++` hints that recursive is more than a simple `bool`. However, it is possible to write the code with a higher level semantic:
+In this simple case, the use of both `recursive` and `++*recursive++` hints that recursive is more than a simple `bool`. However, it is possible to write the code with a higher level semantic (see S6023):
 
 [source,cpp]
 ----
@@ -117,6 +117,11 @@ void perform(optional<bool> recursive) {
 This syntax is more complex, but it is also more flexible, especially when chaining operations on `optional` or `expected` values.
 
 == Resources
+
+=== Related rules
+
+* S6023 - "std::optional" member function "value_or" should be used
+
 === Documentation
 
 * {cpp} reference - https://en.cppreference.com/w/cpp/utility/optional[`std::optional`]