Update docs/getting-started/getting-started-chunks.md (#3027)

Signed-off-by: Brian Pham <[email protected]>

Author: brianpham

docs/getting-started/getting-started-chunks.md

@@ -20,7 +20,10 @@ Cortex can also make use of external memcacheds for caching and although these a
 
 For simplicity and to get started, we'll run it as a [single process](../configuration/single-process-config.md) with no dependencies:
 
+Clone and build prometheus
 ```sh
+$ git clone https://github.com/cortexproject/cortex.git
+$ cd cortex
 $ go build ./cmd/cortex
 $ ./cortex -config.file=./docs/configuration/single-process-config.yaml
 ```