README.md: Clarify C++11 support.
README.md: Clarify C++11 support.

ccpaging/log4cplus,csuideal/log4cplus,csuideal/log4cplus,ccpaging/log4cplus,ccpaging/log4cplus,csuideal/log4cplus,csuideal/log4cplus,ccpaging/log4cplus