Document YAML file schema in README

Add information about the schema in the README file, as we
ask others to provide data.

Change-Id: Iab72e4f8626d766f1b87921c5582668301547b9d

README.rst

@@ -1,3 +1,80 @@
-This repository contains information about OpenStack deliverables,
+=======================
-to be used to generate the OpenStack map and "software" pages on
+ Using This Repository
-the openstack.org website.
+=======================
+
+This repository contains information about OpenStack first-order
+deliverables, to be used to generate the OpenStack map and "software"
+pages on the openstack.org website.
+
+What should be included
+=======================
+
+The goal is to provide a user-facing view of OpenStack deliverables.
+As such, only first-order deliverables (components that users actually
+opt into installing) are presented. Libraries, pure dependencies and
+other second-level deliverables should not be included.
+
+File structure
+==============
+
+This repository contains one file for the OpenStack components themselves
+(openstack_components.yaml), one for tools that can be used to deploy
+them (deployment_tools.yaml) and one for tools that can be used client-side
+to interact with them (sdks.yaml).
+
+Each file has a super-structure with tabs and categories, under which each
+component can be added.
+
+Component schema
+================
+
+Each component is defined by a YAML dictionary with the following keys:
+
+``name``
+  The component name (mandatory).
+
+``title``
+  A user-friendly short description of the component role (mandatory).
+
+``docs-title``
+  Text to use for a link to further documentation (optional).
+
+``docs-url``
+  URL to use for a link to further documentation (optional).
+
+``desc``
+  Long description of the component role (mandatory).
+
+``project-team``
+  Name of the project team that produces this deliverable, as found in
+  the openstack/governance repository in the reference/projects.yaml file
+  (mandatory).
+
+``support-teams``
+  *List* of other project teams (such as I18n, Docs...) to credit for helping
+  in the production of that component, as found in the openstack/governance
+  repository in the reference/projects.yaml file (optional).
+
+``since``
+  First OpenStack release that included that component (optional).
+
+``video``
+  Video to embed. Currently only supports linking to YouTube videos (optional).
+
+  ``id``
+    YouTube ID for the video.
+
+  ``title``
+    Title for the video.
+
+  ``desc``
+    Description of the video.
+
+``dependencies``
+  *List* of other component names that are hard dependencies for this component
+  (can't work without them) (optional, only for openstack_components.yaml).
+
+``see-also``
+  *List* of other component names that are soft dependencies for this component
+  (benefits of the presence of them) (optional, only for
+  openstack_components.yaml).