Update operatoroverloading.dd

Improved formatting by putting some code within text inside "$(D ...)".

operatoroverloading.dd

@@ -596,7 +596,7 @@ void test() {
 	were an array.
 	)
 
-	$(P If an index expression can be rewritten using opIndexAssign or opIndexOpAssign,
+	$(P If an index expression can be rewritten using $(D opIndexAssign) or $(D opIndexOpAssign),
 	those are preferred over opIndex.
 	)
 
@@ -623,8 +623,8 @@ void test() {
 }
 -------
 
-	$(P If a slice expression can be rewritten using opSliceAssign or opSliceOpAssign,
-	those are preferred over opSlice.
+	$(P If a slice expression can be rewritten using $(D opSliceAssign) or $(D opSliceOpAssign),
+	those are preferred over $(D opSlice).
 	)
 
 $(H2 $(LNAME2 Dollar, Dollar Operator Overloading))