Add installation instruction given by official doc

Guides/jenkins.md

@@ -0,0 +1,16 @@
+# Jenkins
+
+How to install and administrate Jenkins.
+
+## Install
+
+### Raspberry Pi
+
+[Jenkins doc : installation](https://jenkins.io/doc/book/installing/#debianubuntu)
+
+```
+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 ;
+```