Add link to conjoined variables details

doc/ci/yaml/README.md

@@ -1265,7 +1265,8 @@ or excluded from a pipeline. In plain English, `if` rules can be interpreted as
 
 `rules:if` differs slightly from `only:variables` by accepting only a single
 expression string per rule, rather than an array of them. Any set of expressions to be
-evaluated can be conjoined into a single expression by using `&&` or `||`, and use
+evaluated can be [conjoined into a single expression](../variables/README.md#conjunction--disjunction)
+by using `&&` or `||`, and use
 the [variable matching syntax](../variables/README.md#syntax-of-environment-variable-expressions).
 
 `if:` clauses are evaluated based on the values of [predefined environment variables](../variables/predefined_variables.md)