Mention C++11 in docs/index.rst as well [ci skip]

Author: dahlia

docs/index.rst

@@ -23,6 +23,12 @@ It's available on PyPI_, so you can install it using :program:`pip`:
 
    $ pip install libsass
 
+.. note::
+
+   libsass-python (and libsass) requires C++11 to compile.
+   It means you need install GCC (G++) 4.8+, LLVM Clang 3.3+,
+   or Visual Studio 2013+.
+
 .. note::
 
    Every release of libsass-python uses the most recent release of Libsass_.