adding note that host-volumes must be defined using absolute paths

Docker-DCO-1.1-Signed-off-by: Will Weaver <monkey@buildingbananas.com> (github: funkymonkeymonk)

AUTHORS

@@ -334,6 +334,7 @@ Wes Morgan <cap10morgan@gmail.com>
 Will Dietz <w@wdtz.org>
 William Delanoue <william.delanoue@gmail.com>
 Will Rouesnel <w.rouesnel@gmail.com>
+Will Weaver <monkey@buildingbananas.com>
 Xiuming Chen <cc@cxm.cc>
 Yang Bai <hamo.by@gmail.com>
 Yurii Rashkovskii <yrashk@gmail.com>

docs/sources/use/working_with_volumes.rst

@@ -90,6 +90,7 @@ Mount a Host Directory as a Container Volume:
 
   -v=[]: Create a bind mount with: [host-dir]:[container-dir]:[rw|ro].
 
+You must specify an absolute path for ``host-dir``.
 If ``host-dir`` is missing from the command, then docker creates a new volume.
 If ``host-dir`` is present but points to a non-existent directory on the host,
 Docker will automatically create this directory and use it as the source of the