Documentation change (#3672)

Co-authored-by: Florian Albrechtskirchinger <falbrechtskirchinger@gmail.com>

docs/examples/from_json__default_constructible.cpp

@@ -0,0 +1,37 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+namespace ns
+{
+// a simple struct to model a person
+struct person
+{
+    std::string name;
+    std::string address;
+    int age;
+};
+} // namespace ns
+
+namespace ns
+{
+void from_json(const json& j, person& p)
+{
+    j.at("name").get_to(p.name);
+    j.at("address").get_to(p.address);
+    j.at("age").get_to(p.age);
+}
+} // namespace ns
+
+int main()
+{
+    json j;
+    j["name"] = "Ned Flanders";
+    j["address"] = "744 Evergreen Terrace";
+    j["age"] = 60;
+
+    auto p = j.get<ns::person>();
+
+    std::cout << p.name << " (" << p.age << ") lives in " << p.address << std::endl;
+}