Update source install deps

README.rst

@@ -83,14 +83,23 @@ supports Python 2.7/3.5+ and PyPy3.5-v5.8.1+.
 If you are on a system that doesn't have a precompiled binary wheel (e.g. FreeBSD)
 then pip will fetch source to build yourself. You must have the necessary packages.
 
-On Debian/Ubuntu for example the necessary packages are:
-
-- build-essential
-- automake
-- pkg-config
-- libtool
-- libffi-dev
-- libgmp-dev (optional)
+On Debian/Ubuntu the necessary system packages are:
+
+- ``build-essential``
+- ``automake``
+- ``pkg-config``
+- ``libtool``
+- ``libffi-dev``
+- ``python3-dev`` (or ``python-dev`` for Python 2)
+- ``libgmp-dev`` (optional)
+
+On macOS the necessary Homebrew packages are:
+
+- ``automake``
+- ``pkg-config``
+- ``libtool``
+- ``libffi``
+- ``gmp`` (optional)
 
 API
 ---