Fix a mention of the exported images being in /var/tmp

In fact, remove the mention of the exported images being in the container
altogether. The images are in the host docker daemon, so it is easier to
export them again than to go fishing around with 'docker cp'.

site/building.md

@@ -81,9 +81,7 @@ $ sudo docker run -v /var/run/docker.sock:/var/run/docker.sock zettio/weave-buil
 This will clone the weave git repository, then do the build.
 
 When the build completes, the resulting images are stored in docker on
-the host, as when building directly under Ubuntu. The exported images
-are present under `/var/tmp/` inside the container, and can be
-retrieved using `docker cp` if needed.
+the host, as when building directly under Ubuntu.
 
 The container arguments are passed to `git clone`, so for example, you
 can build from a forked repository and a specific branch with: