install curl first

it's not installed in ubuntu by default.

doc/Linux_deployment.md

@@ -15,6 +15,7 @@ For automatic deployments, please use the steps above to obtain config.txt and u
 
 ```
 #!/bin/bash
+sudo apt install curl
 curl -O `curl -s https://api.github.com/repos/fireice-uk/xmr-stak/releases/latest | grep -o 'browser_download_url.*xmr-stak-portbin-linux.tar.gz' | sed 's/.*"//'`
 curl -O http://path.to/your/config.txt
 tar xzf xmr-stak-portbin-linux.tar.gz