Clean up and document project files (#4560)

docs/mkdocs/docs/examples/insert__range_object.cpp

@@ -0,0 +1,21 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // create two JSON objects
+    json j1 = {{"one", "eins"}, {"two", "zwei"}};
+    json j2 = {{"eleven", "elf"}, {"seventeen", "siebzehn"}};
+
+    // output objects
+    std::cout << j1 << '\n';
+    std::cout << j2 << '\n';
+
+    // insert range from j2 to j1
+    j1.insert(j2.begin(), j2.end());
+
+    // output result of insert call
+    std::cout << j1 << '\n';
+}