Make it clear you need to clone & cd into the repo.

Signed-off-by: Tom Wilkie <[email protected]>

Author: tomwilkie

README.md

@@ -60,6 +60,8 @@ To generate the Grafana dashboards and Prometheus alerts for Cortex:
 ```console
 $ GO111MODULE=on go get github.com/monitoring-mixins/mixtool/cmd/mixtool
 $ GO111MODULE=on go get github.com/jsonnet-bundler/jsonnet-bundler/cmd/jb
+$ git clone https://github.com/grafana/cortex-jsonnet
+$ cd cortex-jsonnet
 $ make build-mixin
 ```