[lxc] add some words of warning around edge cases

website/source/docs/builders/lxc.html.md

@@ -18,6 +18,11 @@ as a tar.gz of the root file system.
 The LXC builder requires a modern linux kernel and the `lxc` or `lxc1` package.
 This builder does not work with LXD.
 
+Note to build Centos images on a Debian family host, you will need the `yum` package installed.
+
+Some provisioners such as `ansible-local` get confused when running in a container of a different family.
+E.G. it will attempt to use `apt-get` to install packages, when running in a Centos container if the parent OS is Debian based.
+
 ## Basic Example
 
 Below is a fully functioning example.