Update FAQ to add RPI explainations

docs/faq.rst

@@ -57,6 +57,18 @@ a load balancer.
 
 The only problem is a lack of support for ARM. But there's a ticket opened on their JIRA issue tracker.
 
+Can I install LISA on a Raspberry Pi ?
+--------------------------------------
+Quick answer : Yes.
+
+Long answer : RPI is an ARM architecture and actually Mongodb is unsupported officially.
+So it isn't packaged for raspbian for example. But you should be able to compile it (take ~7hours).
+
+There's a ticket already opened on their JIRA for ARM support, and they are working on it.
+
+By now, I suggest to run mongodb (and the LISA server) in a virtual machine or a dedicated x86 server.
+
+
 What ports should I open on my firewall ?
 -----------------------------------------
 
@@ -72,4 +84,4 @@ Why LISA is written in Python ?
 -------------------------------
 Firstly, I wanted to learn this language since a long. The code may be not perfect so don't hesit to send a patch.
 I love Python because there's a lot of API written in Python language and as LISA is a built to connect API between them
-it was logic to use a language easy to learn and easy to use.
+it was logic to use a language easy to learn and easy to use.