READMEs for software-config templates and hooks

Change-Id: Idf2be681f26f13da7eeaee38ada73a2be4440575

hot/software-config/elements/README.rst

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+============================
+Software configuration hooks
+============================
+
+This directory contains `diskimage-builder <https://github.com/openstack/diskimage-builder>`_
+elements to build an image which contains the software configuration hook
+required to use your preferred configuration method.
+
+These elements depend on some elements found in the
+`tripleo-image-elements <https://github.com/openstack/tripleo-image-elements>`_
+repository. These elements will build an image which uses
+`os-collect-config <https://github.com/openstack/os-collect-config>`_,
+`os-refresh-config <https://github.com/openstack/os-refresh-config>`_, and
+`os-apply-config <https://github.com/openstack/os-apply-config>`_ together to
+invoke a hook with the supplied configuration data, and return any outputs back
+to heat.
+
+When building an image, the heat-config element is required, along with the elements
+for the hooks which enable the preferred configuration methods.
+
+An example fedora based image containing all hooks can be built and uploaded to glance
+with the following:
+
+::
+
+  git clone https://git.openstack.org/openstack/diskimage-builder.git
+  git clone https://git.openstack.org/openstack/tripleo-image-elements.git
+  git clone https://git.openstack.org/openstack/heat-templates.git
+  export ELEMENTS_PATH=tripleo-image-elements/elements:heat-templates/hot/software-config/elements
+  diskimage-builder/bin/disk-image-create vm \
+    fedora \
+    heat-config \
+    os-collect-config \
+    os-refresh-config \
+    os-apply-config \
+    heat-config-cfn-init \
+    heat-config-puppet \
+    heat-config-script \
+    -o fedora-software-config.qcow2
+  glance image-create --disk-format qcow2 --container-format bare --name fedora-software-config < \
+    fedora-software-config.qcow2