README: OS X -> macOS (GH-55)

Author: paulschreiber

README.rst

@@ -35,7 +35,7 @@ Installable Python kits, and information about using Python, are available at
 Build Instructions
 ------------------
 
-On Unix, Linux, BSD, OSX, and Cygwin::
+On Unix, Linux, BSD, macOS, and Cygwin::
 
     ./configure
     make
@@ -45,10 +45,10 @@ On Unix, Linux, BSD, OSX, and Cygwin::
 This will install Python as python3.
 
 You can pass many options to the configure script; run ``./configure --help``
-to find out more.  On OSX and Cygwin, the executable is called ``python.exe``;
+to find out more.  On macOS and Cygwin, the executable is called ``python.exe``;
 elsewhere it's just ``python``.
 
-On Mac OS X, if you have configured Python with ``--enable-framework``, you
+On macOS, if you have configured Python with ``--enable-framework``, you
 should use ``make frameworkinstall`` to do the installation.  Note that this
 installs the Python executable in a place that is not normally on your PATH,
 you may want to set up a symlink in ``/usr/local/bin``.