Clean up and document project files (#4560)

docs/mkdocs/docs/examples/json_lines.cpp

@@ -0,0 +1,22 @@
+#include <sstream>
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // JSON Lines (see https://jsonlines.org)
+    std::stringstream input;
+    input << R"({"name": "Gilbert", "wins": [["straight", "7♣"], ["one pair", "10♥"]]}
+{"name": "Alexa", "wins": [["two pair", "4♠"], ["two pair", "9♠"]]}
+{"name": "May", "wins": []}
+{"name": "Deloise", "wins": [["three of a kind", "5♣"]]}
+)";
+
+    std::string line;
+    while (std::getline(input, line))
+    {
+        std::cout << json::parse(line) << std::endl;
+    }
+}