added another insert function

doc/examples/insert__ilist.cpp

@@ -0,0 +1,16 @@
+#include <json.hpp>
+
+using namespace nlohmann;
+
+int main()
+{
+    // create a JSON array
+    json v = {1, 2, 3, 4};
+
+    // insert range from v2 before the end of array v
+    auto new_pos = v.insert(v.end(), {7, 8, 9});
+
+    // output new array and result of insert call
+    std::cout << *new_pos << '\n';
+    std::cout << v << '\n';
+}