Add make targets for build and release for ARM macs. (grundleborg#27)

Makefile

@@ -1,4 +1,4 @@
-.PHONY: build build-linux build-mac build-windows release clean
+.PHONY: build build-linux build-mac build-mac-arm build-windows release clean
 
 ROOT := $(dir $(abspath $(lastword $(MAKEFILE_LIST))))
 
@@ -13,6 +13,10 @@ build-mac: ## Build Slack Advanced Exporter for Mac
 	@mkdir -p ${ROOT}build
 	cd ${ROOT}build && GOOS=darwin GOARCH=amd64 go build ..
 
+build-mac-arm: ## Build Slack Advanced Exporter for ARM Mac
+	@mkdir -p ${ROOT}build
+	cd ${ROOT}build && GOOS=darwin GOARCH=arm64 go build ..
+
 build-windows: ## Build Slack Advanced Exporter for Windows
 	@mkdir -p ${ROOT}build
 	cd ${ROOT}build && GOOS=windows GOARCH=amd64 go build ..
@@ -24,6 +28,8 @@ release: clean ## Build and package the release artefacts
 	cd ${ROOT}build && tar -czf ../release/slack-advanced-exporter.linux-amd64.tar.gz slack-advanced-exporter
 	cd ${ROOT}build && GOOS=darwin GOARCH=amd64 go build ..
 	cd ${ROOT}build && tar -czf ../release/slack-advanced-exporter.darwin-amd64.tar.gz slack-advanced-exporter
+	cd ${ROOT}build && GOOS=darwin GOARCH=arm64 go build ..
+	cd ${ROOT}build && tar -czf ../release/slack-advanced-exporter.darwin-arm64.tar.gz slack-advanced-exporter
 	cd ${ROOT}build && GOOS=windows GOARCH=amd64 go build ..
 	cd ${ROOT}build && zip -q ../release/slack-advanced-exporter.windows-amd64.zip slack-advanced-exporter.exe
 	cd ${ROOT}release && sha256sum ./slack-advanced-exporter.*