Document logging configuration

[cen1]

Please add minimum documentation on how to configure logging. Suggested page:
https://github.com/sony/easyhttpcpp/wiki/Recipe:-Configuring-EasyHttp

Example:

easyhttpcpp::common::CoreLogger::getInstance()->setLoggingLevel(easyhttpcpp::common::LogLevel::LogLevelWarning);