bump Intel compiler version requirement

Author: wjakob

README.md

@@ -89,7 +89,7 @@ In addition to the core functionality, pybind11 provides some extra goodies:
 1. Clang/LLVM (any non-ancient version with C++11 support)
 2. GCC (any non-ancient version with C++11 support)
 3. Microsoft Visual Studio 2015 or newer
-4. Intel C++ compiler v15 or newer
+4. Intel C++ compiler 16 or newer (15 with a [workaround](https://github.com/pybind/pybind11/issues/276))
 5. Cygwin/GCC (tested on 2.5.1)
 
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