Docs: Added a command to start elasticsearch on bootup on Debian.

Close #8600

docs/reference/setup/repositories.asciidoc

@@ -30,7 +30,12 @@ Run apt-get update and the repository is ready for use. You can install it with
 apt-get update && apt-get install elasticsearch
 --------------------------------------------------
 
+Configure Elasticsearch to automatically start during bootup :
 
+[source,sh]
+--------------------------------------------------
+sudo update-rc.d elasticsearch defaults 95 10
+--------------------------------------------------
 
 [float]
 === YUM