Replace message by a lighter caution

Author: pasdeloup

book/installation.rst

@@ -229,8 +229,11 @@ If there are any issues, correct them now before moving on.
     its user to be the same as your CLI user (e.g. for Apache, update the ``User``
     and ``Group`` values).
 
-    Be careful, this option is not recommended on production environments for security
-    reasons as a compromise server would give to the hacker the same privileges than this user.
+    .. caution::
+    
+      If used in a production environment, be sure this user only has limited privileges
+      (no access to private data or servers, launch of unsafe binaries, etc.)
+      as a compromised server would give to the hacker those privileges.
 
     **2. Using ACL on a system that supports chmod +a**