Rework Mac port to be more Linux-like without needing to launch XCode. See

macos/README.txt for information.

macos/README.txt

@@ -0,0 +1,49 @@
+WHAT IS THIS
+------------
+This document describes how to build Tux Paint for macOS 10.12 Sierra and later.
+
+Tux Paint 0.9.22 and earlier required building Tux Paint from the XCode IDE.
+Starting with 0.9.23, however, Tux Paint for macOS is built as though it were a
+Linux application.
+
+
+REQUIREMENTS
+------------
+Although Tux Paint is run without the XCode IDE, XCode itself is still required
+to build Tux Paint. Download it from the App Store, and launch it once to
+accept its license agreements.
+
+Building Tux Paint also requires various libraries from MacPorts.  Install them
+to the default /opt/local path according to the instructions found on their
+website:
+
+  https://www.macports.org/
+
+As of this writing, the required libraries are:
+
+  cairo
+  fribidi
+  libpaper
+  libpng
+  librsvg
+  libsdl
+  libsdl_image
+  libsdl_mixer
+  libsdl_pango
+  libsdl_ttf
+  zlib
+
+... but you should intall any package that is required by the latest version of
+Tux Paint.
+
+
+HOW TO BUILD
+------------
+Simply, run:
+
+  % make
+  % make install
+
+... to create the TuxPaint.app application bundle that can be run in-place or
+copied to /Applications.  Zip it up for distribution.
+