Add some basic evironment docs

Change-Id: I6edbb7da0d333bd86eabba73631d5df3d4dc8328

doc/source/template_guide/environment.rst

@@ -0,0 +1,79 @@
+..
+      Licensed under the Apache License, Version 2.0 (the "License"); you may
+      not use this file except in compliance with the License. You may obtain
+      a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+      Unless required by applicable law or agreed to in writing, software
+      distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+      WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+      License for the specific language governing permissions and limitations
+      under the License.
+
+============
+Environments
+============
+
+The environment is used to affect the runtime behaviour of the
+template. It provides a way to override the default resource
+implementation and the parameters passed to Heat.
+
+------
+Format
+------
+It is a yaml text file with two main sections "resource_registry" and "parameters".
+
+------------------
+Command line usage
+------------------
+::
+
+  heat stack-create -e my_env.yaml -P "some_parm=bla" -f my_tmpl.yaml
+
+--------------
+Usage examples
+--------------
+
+1) Pass parameters into Heat
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+::
+
+  parameters:
+    KeyName: heat_key
+    InstanceType: m1.micro
+    ImageId: F18-x86_64-cfntools
+
+
+2) Deal with the renaming of Quantum to Neutron
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+::
+
+  resource_registry:
+    "OS::Quantum*": "OS::Neutron*"
+
+
+3) Override a resource type with a custom TemplateResource
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+::
+
+  resource_registry:
+    "AWS::EC2::Instance": file:///home/mine/my_instance_with_better_defaults.yaml
+
+
+4) Always map resource type X to Y
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+::
+
+  resource_registry:
+    "OS::Networking::FloatingIP": "OS::Nova::FloatingIP"
+
+
+5) Use default resources except one for a particular resource in the template
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+::
+
+  resource_registry:
+    resources:
+      my_db_server:
+        "OS::DBInstance": file:///home/mine/all_my_cool_templates/db.yaml

doc/source/template_guide/index.rst

@@ -17,6 +17,7 @@ Template Guide
 .. toctree::
    :maxdepth: 2
 
+   environment
    functions
    openstack
    cfn