introduce 'host' permission + docs

Fixes: https://pagure.io/koji/issue/1453

docs/source/index.rst

@@ -22,6 +22,7 @@ Contents
     :maxdepth: 2
 
     HOWTO
+    permissions
     defining_hub_policies
     external_repo_server_bootstrap
     image_build

docs/source/permissions.rst

@@ -0,0 +1,76 @@
+=================
+Permission system
+=================
+
+Basic privileges for koji are handled by ``permissions``. These are granted
+and removed by ``admin`` user and allows other users to use different parts
+of koji. There are some default permissions, but new ones can be created by
+administrator and used in koji's :doc:`policies <defining_hub_policies>` or tag
+locks.
+
+Permission management
+=====================
+
+Admin user can use following koji CLI commands:
+
+  * ``koji grant-permission [--new] <permission> <user> [<user> ...]`` for
+    granting permission to one or more users. It can be also used to create
+    new permission class with ``--new``.
+  * ``koji revoke-permission <permission> <user> [<user> ...]`` for removing
+    such permission from users.
+  * ``koji list-permissions [--user <user>] [--mine]`` is self-descriptive.
+
+Default permissions
+===================
+
+Administration
+--------------
+
+``admin``
+  Basic permission, which can be delegated to other users. This
+  is superadmin without any limitations, so grant with caution. Especially
+  services should use some limited form instead of this.
+
+``host``
+  Restricted permission for handling host-related management tasks.
+
+Tasks
+-----
+
+``appliance``
+  appliance tasks (``koji spin-appliance``)
+
+``build``
+  currently unused
+
+``dist-repo``
+  distRepo tasks (``koji dist-repo``)
+
+``image``
+  image tasks (``koji image-build``)
+
+``livecd``
+  livecd tasks (``koji spin-livecd``)
+
+``repo``
+  newRepo tasks (``koji regen-repo``)
+
+``regen-repo``
+  same as ``repo`` for now
+
+Data
+----
+``image-import``
+  used for importing external maven artifacts
+  (``koji import-archive --type maven``)
+
+``maven-import``
+  used for importing external maven artifacts
+  (``koji import-archive --type maven``)
+
+``win-admin``
+  used in default policy for windows builds ('vm' channel)
+
+``win-import``
+  used for importing external maven artifacts
+  (``koji import-archive --type win``)