[libcxx] Mentions "targeting C++11 and above" instead of "targeting C++11" in the doc

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@293071 91177308-0d34-0410-b5e6-96231b3b80d8

docs/index.rst

@@ -7,7 +7,8 @@
 Overview
 ========
 
-libc++ is a new implementation of the C++ standard library, targeting C++11.
+libc++ is a new implementation of the C++ standard library, targeting C++11 and
+above.
 
 * Features and Goals