added link for merge.md

Author: rotarymars

reference/algorithm/merge.md

@@ -126,6 +126,10 @@ int main()
 * b.end()[link /reference/vector/vector/end.md]
 * result.begin()[link /reference/vector/vector/begin.md]
 * result.end()[link /reference/vector/vector/end.md]
+* std::back_inserter[link /reference/iterator/back_inserter.md]
+* std::cout[link /reference/iostream/cout.md]
+* std::endl[link /reference/ostream/endl.md]
+* std::for_each[link /reference/algorithm/for_each.md]
 
 ### 出力
 ```