Add link, tweak default opEquals wording

Author: ntrel

spec/expression.dd

@@ -681,8 +681,8 @@ $(GNAME EqualExpression):
 
     $(P For struct objects, equality means the result of the
         $(LINK2 https://dlang.org/spec/operatoroverloading.html#equals, `opEquals()` member function).
-        If an `opEquals()` is not provided, equality is defined as
-        the logical product of all equality
+        If an `opEquals()` is not provided, one will be generated.
+        Equality is defined as the logical product of all equality
         results of the corresponding object fields.
     )
 

spec/operatoroverloading.dd

@@ -388,7 +388,8 @@ $(H2 $(LNAME2 eqcmp, Overloading the Comparison Operators))
 
         $(P Therefore, it is the programmer's responsibility to ensure that
         `opCmp` and $(D opEquals) are consistent with each other. If
-        `opEquals` is not specified, the compiler provides a default version for structs
+        `opEquals` is not specified for a struct, the compiler provides a
+        $(DDSUBLINK spec/expression, struct_equality, default version) of it
         that does member-wise comparison. If this suffices, one may define only
         $(D opCmp) to customize the behaviour of the *RelExpression* operators.  But
         if not, then a custom version of $(D opEquals) should be defined as