Added build instructions for MacOS

README.md

@@ -137,6 +137,34 @@ If all worked out correctly you can now use IfcOpenShell. See the examples below
 
     $ sudo make install
     
+### Installing on MacOS Using Homebrew
+
+**1)** Install all dependencies using [Homebrew](https://brew.sh/)
+
+```{shell}
+$ brew install boost swig cmake ftgl cgal gmp libaec opencascade
+```
+
+**2)** Clone the git repo and its submodules
+```{shell}
+$ git clone --recurse-submodules https://github.com/IfcOpenShell/IfcOpenShell.git 
+```
+**3)** Build IfcOpenShell with flags for Homebrew dependencies (```/usr/local/```)
+```{shell}
+$ cd /path/to/IfcOpenShell
+$ mkdir build && cd build
+$ cmake ../cmake -DOCC_LIBRARY_DIR=/usr/local/lib/ \
+      -DOCC_INCLUDE_DIR=/usr/local/include/opencascade/ \
+      -DCOLLADA_SUPPORT=0 \
+      -DCGAL_INCLUDE_DIR=/usr/local/include/ \
+      -DGMP_LIBRARY_DIR=/usr/local/lib/ \
+      -DMPFR_LIBRARY_DIR=/usr/local/lib/
+      
+$ make -j -lboost_options
+```
+
+Note: Make sure to compile using XCode, rather than a ```brew``` installed C/C++ compiler.
+
 Installing IfcOpenShell with Conda
 ----------------------------------
 Another option for building and installing IfcOpenShell is to use the popular