Clarified instructions for installing Xcode and gcc on Mac OS X.

README.rst

@@ -104,7 +104,7 @@ Linux
 macOS
 ^^^^^
 
-* Xcode (the IDE for macOS) comes with the LLVM (clang) compiler, but it does not currently support OpenMP, so you must install `gcc <https://gcc.gnu.org>`_. This can be done by downloading and installing the `Homebrew package manager <http://brew.sh>`_ and running:
+* Xcode (the IDE for macOS) comes with the LLVM (clang) compiler, but it does not currently support OpenMP, so you must install `gcc <https://gcc.gnu.org>`_. That said, it is still useful to have Xcode (with command line tools) installed. It can be downloaded from the App Store. Once Xcode is installed, download and install the `Homebrew package manager <http://brew.sh>`_ and then to install gcc, run:
 
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