Add recipe for installing mosh from ppa

Mosh 1.4.0 isn't yet in all package repos and includes truecolor support

recipes/default/mosh_ppa

@@ -0,0 +1,8 @@
+#! /bin/bash
+
+set -e
+
+sudo add-apt-repository ppa:keithw/mosh-dev
+sudo apt-get update
+
+sudo apt-get install -y mosh