update readme for OSX install

Author: arifogel

README.batfish

@@ -6,6 +6,13 @@ LINUX_BASE=ubuntu_14.04 TRAVIS_OS_NAME=linux contrib/ci/scripts/travis_ci_entry_
 ## Ubuntu 16,04 (USES DOCKER)
 LINUX_BASE=ubuntu_16.04 TRAVIS_OS_NAME=linux contrib/ci/scripts/travis_ci_entry_point.sh
 
+### OSX
+# For all OSX builds as of Mojave, make sure you have installed SDK headers by executing:
+# open /Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg
+#
+# You may need to install other dependencies via:
+# contrib/ci/scripts/install_deps_osx.sh
+#
 ## OSX with OpenMP (RECOMMENDED, MUST BE RUN ON OSX, DOES NOT USE DOCKER)
 ./package_z3_osx_openmp.sh