Merge pull request #2455 from hashicorp/doc-load-upgrade

Mention #2361 in upgrade notes.

website/source/docs/upgrade/upgrade-specific.html.md

@@ -15,6 +15,17 @@ details provided for their upgrades as a result of new features or changed
 behavior. This page is used to document those details separately from the
 standard upgrade flow.
 
+## Nomad 0.5.5
+
+Nomad 0.5.5 has a backward incompatible change in the `docker` driver's
+configuration. Prior to 0.5.5 the `load` configuration option accepted a list
+images to load, in 0.5.5 it has been changed to a single string. No
+functionality was changed. Even if more than one item was specificed prior to
+0.5.5 only the first item was used.
+
+If you have jobs that use the `load` option first upgrade all nodes to 0.5.5,
+then resubmit those jobs with `load` as a single string.
+
 ## Nomad 0.4.0
 
 Nomad 0.4.0 has backward incompatible changes in the logic for Consul