Add note about host-only networking

Author: velvia

doc/docker.md

@@ -88,3 +88,7 @@ Example Marathon config, thanks to @peterklipfel:
 ### I can't access a textfile
 
 You might not be able to access HDFS, or whatever shared file system your data files are on.  Make sure the right ports are open.  Also see https://github.com/spark-jobserver/spark-jobserver/issues/243#issuecomment-168242345.
+
+### Timeouts
+
+You may need to enable host-only networking to get Docker to work in AWS.