Add documentation for the Tmpfs Hostconfig option.

Signed-off-by: Jan Losinski <losinski@wh2.tu-dresden.de>

docs/hostconfig.md

@@ -111,6 +111,8 @@ for example:
   container process will run as.
 * devices (list): Host device bindings. See [host devices](host-devices.md)
   for more information.
+* tmpfs: Temporary filesystems to mouunt. See [Using tmpfs](tmpfs.md) for more
+  information.
 
 **Returns** (dict) HostConfig dictionary
 

docs/tmpfs.md

+# Using Tmpfs
+
+Tmpfs declaration is done with the `Client().create_container()`
+method by declaring the mountpoints in the `host_config` section.
+
+This is available from docker 1.10.
+
+You can provide a list of declarations similar to the `--tmpfs`
+option of the docker commandline client:
+
+```python
+container_id = cli.create_container(
+    'busybox', 'ls',
+    host_config=cli.create_host_config(tmpfs=[
+        '/mnt/vol2',
+        '/mnt/vol1:size=3G,uid=1000'
+    ])
+)
+```
+
+You can alternatively specify tmpfs as a dict the docker remote
+API uses:
+
+```python
+container_id = cli.create_container(
+    'busybox', 'ls',
+    host_config=cli.create_host_config(tmpfs={
+        '/mnt/vol2': '',
+        '/mnt/vol1': 'size=3G,uid=1000'
+    })
+)
+```