🐛 fixed README example

The example with the size() operator is bad: using operator[] already
changes the size of the object. The fix makes it clearer.

doc/examples/README.cpp

@@ -1,4 +1,5 @@
 #include <json.hpp>
+#include <iomanip> // for std::setw
 
 using json = nlohmann::json;
 
@@ -29,7 +30,8 @@ int main()
     j["new"]["key"]["value"] = {"another", "list"};
 
     // count elements
-    j["size"] = j.size();
+    auto s = j.size();
+    j["size"] = s;
 
     // pretty print with indent of 4 spaces
     std::cout << std::setw(4) << j << '\n';

doc/examples/README.output

@@ -1,27 +0,0 @@
-{
-    "answer": {
-        "everything": 42
-    },
-    "happy": true,
-    "list": [
-        1,
-        0,
-        2
-    ],
-    "name": "Niels",
-    "new": {
-        "key": {
-            "value": [
-                "another",
-                "list"
-            ]
-        }
-    },
-    "nothing": null,
-    "object": {
-        "currency": "USD",
-        "value": 42.99
-    },
-    "pi": 3.141,
-    "size": 9
-}