📝 added example and documentation for the meta function

doc/examples/meta.cpp

@@ -0,0 +1,9 @@
+#include <json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // call meta()
+    std::cout << std::setw(4) << json::meta() << '\n';
+}