Fixed warning for example

example/example.cpp

@@ -136,11 +136,11 @@ void callback_example()
     });
 }
 
-#include "spdlog/cfg/env.h"
 void load_levels_example()
 {
     // Set the log level to "info" and mylogger to "trace":
     // SPDLOG_LEVEL=info,mylogger=trace && ./example
+    // must #include "spdlog/cfg/env.h"
     spdlog::cfg::load_env_levels();
     // or from command line:
     // ./example SPDLOG_LEVEL=info,mylogger=trace