Documentation change (#3672)

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

docs/examples/to_json.cpp

@@ -0,0 +1,32 @@
+#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 to_json(json& j, const person& p)
+{
+    j = json{ {"name", p.name}, {"address", p.address}, {"age", p.age} };
+}
+} // namespace ns
+
+int main()
+{
+    ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
+
+    json j = p;
+
+    std::cout << j << std::endl;
+}