Add arm64 build (#108)

Signed-off-by: Marcus Sorensen <mls@apple.com>

Co-authored-by: Marcus Sorensen <mls@apple.com>

Makefile

diff --git a/Makefile b/Makefile
index 014dc98..b54b956 100644
--- a/Makefile
+++ b/Makefile
@@ -63,6 +63,7 @@
 	GOOS=windows GOARCH=386 $(GO) build -mod=vendor -ldflags='-s -w -X main.GitSHA=$(GIT_SHA) -X main.BuildDate=$(DATE)' -o dist/cmk.windows.x86.exe cmk.go
 	GOOS=windows GOARCH=amd64 $(GO) build -mod=vendor -ldflags='-s -w -X main.GitSHA=$(GIT_SHA) -X main.BuildDate=$(DATE)' -o dist/cmk.windows.x86-64.exe cmk.go
 	GOOS=darwin  GOARCH=amd64 $(GO) build -mod=vendor -ldflags='-s -w -X main.GitSHA=$(GIT_SHA) -X main.BuildDate=$(DATE)' -o dist/cmk.darwin.x86-64 cmk.go
+	GOOS=darwin  GOARCH=arm64 $(GO) build -mod=vendor -ldflags='-s -w -X main.GitSHA=$(GIT_SHA) -X main.BuildDate=$(DATE)' -o dist/cmk.darwin.arm64 cmk.go
 
 # Tools