Update readFromString.cpp (#1477)

Print the error to screen

Co-authored-by: Jordan Bayles <bayles.jordan@gmail.com>
diff --git a/example/readFromString/readFromString.cpp b/example/readFromString/readFromString.cpp
index 0b29a4e..878f9eb 100644
--- a/example/readFromString/readFromString.cpp
+++ b/example/readFromString/readFromString.cpp
@@ -25,7 +25,7 @@
     const std::unique_ptr<Json::CharReader> reader(builder.newCharReader());
     if (!reader->parse(rawJson.c_str(), rawJson.c_str() + rawJsonLength, &root,
                        &err)) {
-      std::cout << "error" << std::endl;
+      std::cout << "error: " << err << std::endl;
       return EXIT_FAILURE;
     }
   }