Add Makefile to build xcframework

Makefile

@@ -0,0 +1,9 @@
+.PHONY: frameworks
+
+CWD := $(abspath $(patsubst %/,%,$(dir $(abspath $(lastword $(MAKEFILE_LIST))))))
+
+frameworks:
+	$(CWD)/scripts/build-framework.sh
+	@echo "Framework built in $(CWD)/CryptoSwift.xcframework"
+
+all: frameworks