file_copy: Add documentation

bootstrapvz/plugins/file_copy/README.rst

@@ -0,0 +1,26 @@
+File copy
+---------
+
+This plugin lets you copy files from the host to the VM under construction,
+  create directories, and set permissions and ownership.
+
+Note that this necessarily violates the `first development guideline`_.
+
+.. _first development guideline: https://github.com/andsens/bootstrap-vz/blob/master/CONTRIBUTING.rst#the-manifest-should-always-fully-describe-the-resulting-image
+
+
+Settings
+~~~~~~~~
+
+The ``file_copy`` plugin takes a (non-empty) ``files`` list, and optionnaly a ``mkdirs`` list.
+
+Files (items in the ``files`` list) must be objects with the following properties:
+* ``src`` and ``dst`` (required) are the source and destination paths.
+  ``src`` is relative to the current directory, whereas ``dst`` is a path in the VM.
+* ``permissions`` (optional) is a permission string in a format appropriate for ``chmod(1)``.
+* ``owner`` and ``group`` (optional) are respectively a user and group specification,
+  in a format appropriate for ``chown(1)`` and ``chgrp(1)``.
+
+Folders (items in the ``mkdirs`` list) must be objects with the following properties:
+* ``dir`` (required) is the path of the directory.
+* ``permissions``, ``owner`` and ``group`` are the same as for files.