Add bindtab docs

userguide/advanced/exposing_host_directories.rst

@@ -0,0 +1,19 @@
+Exposing host directories
+=========================
+
+Anbox reads a file similar to ``fstab`` called ``bindtab`` from ``<data-path>/bindtab`` (for example ``/var/snap/anbox/bindtab``) to bind directories in the android file system to those on the host.
+The file follows the ``fstab`` format with a few extra options described in the ``lxc.mount.entry`` section in the `LXC documentation <https://linuxcontainers.org/lxc/manpages/man5/lxc.container.conf.5.html>`_.
+The file is read and passed to the internal LXC configuration.
+It does not support inline comments and the host directory should be an absolute path.
+
+Example:
+
+.. code-block:: text
+
+    # This file doesn't support inline comments
+    # and it requires an absolute path for the host directory
+
+    # <host>   <target in anbox> <type> <options>                   <dump>  <pass>
+    /home/data data/media/0/data none   bind,create=dir,optional    0       0
+
+

userguide/advanced/index.rst

@@ -10,3 +10,4 @@ This section of the documentation details advanced tasks that power users may wa
     rootfs_overlay
     software_rendering
     network_configuration
+    exposing_host_directories