Add some insights about file locations

Where to run commands, logs, and configuration

Guides/jenkins.md

@@ -8,9 +8,21 @@ How to install and administrate Jenkins.
 
 [Jenkins doc : installation](https://jenkins.io/doc/book/installing/#debianubuntu)
 
+To execute on debian server
+
 ```
 wget -q -O - https://pkg.jenkins.io/debian/jenkins.io.key | sudo apt-key add - ;
 sudo sh -c 'echo deb https://pkg.jenkins.io/debian-stable binary/ > /etc/apt/sources.list.d/jenkins.list' ;
 sudo apt-get update ;
 sudo apt-get install jenkins ;
 ```
+
+## Trouble shooting
+
+### Logs
+
+In file `/var/log/jenkins/jenkins.log` 
+
+## Configure
+
+Configuration parameters can be found at `/etc/default/jenkins`