update contributing link

Makefile

@@ -91,7 +91,7 @@ testrace: deps ## Test for race conditions
 	@go test -race $(TEST) $(TESTARGS) -timeout=2m
 
 updatedeps:
-	@echo "INFO: Packer deps are managed by govendor. See CONTRIBUTING.md"
+	@echo "INFO: Packer deps are managed by govendor. See .github/CONTRIBUTING.md"
 
 help:
 	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | sort | awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m%-30s\033[0m %s\n", $$1, $$2}'

README.md

@@ -43,8 +43,10 @@ for those with a bit more patience. Otherwise, the quick start below
 will get you up and running quickly, at the sacrifice of not explaining some
 key points.
 
-First, [download a pre-built Packer binary](https://www.packer.io/downloads.html)
-for your operating system or [compile Packer yourself](CONTRIBUTING.md#setting-up-go-to-work-on-packer).
+First, [download a pre-built Packer
+binary](https://www.packer.io/downloads.html) for your operating system or
+[compile Packer
+yourself](https://github.com/hashicorp/packer/blob/master/.github/CONTRIBUTING.md#setting-up-go-to-work-on-packer).
 
 After Packer is installed, create your first template, which tells Packer
 what platforms to build images for and how you want to build them. In our