ci: set up a macos host Script to set up dependencies on a macOS build system.
diff --git a/ci/setup-macos.sh b/ci/setup-macos.sh
new file mode 100755
index 0000000..a906691
--- /dev/null
+++ b/ci/setup-macos.sh
@@ -0,0 +1,6 @@
+#!/bin/sh
+
+set -x
+
+brew update
+brew install pkgconfig zlib curl openssl libssh2