Add strategy template doc

Developer should provide a detailled documentation about his strategy
algorithm to make it even easier to use by a Watcher end user.
I propose in this changeset a template for strategy documentation.
you will find also a example with basic consolidation strategy.

Change-Id: I66da1a33b87a94b508dd23ac7dce4cae6f4e068b

doc/source/strategies/basic-server-consolidation.rst

@@ -0,0 +1,96 @@
+==================================
+Basic Offline Server Consolidation
+==================================
+
+Synopsis
+--------
+
+**display name**: ``basic``
+
+**goal**: ``server_consolidation``
+
+    .. watcher-term:: watcher.decision_engine.strategy.strategies.basic_consolidation
+
+Requirements
+------------
+
+Metrics
+*******
+
+The *basic* strategy requires the following metrics:
+
+============================ ============ ======= =======
+metric                       service name plugins comment
+============================ ============ ======= =======
+``compute.node.cpu.percent`` ceilometer_  none
+``cpu_util``                 ceilometer_  none
+============================ ============ ======= =======
+
+.. _ceilometer: http://docs.openstack.org/admin-guide/telemetry-measurements.html#openstack-compute
+
+Cluster data model
+******************
+
+Default Watcher's Compute cluster data model:
+
+    .. watcher-term:: watcher.decision_engine.model.collector.nova.NovaClusterDataModelCollector
+
+Actions
+*******
+
+Default Watcher's actions:
+
+
+    .. list-table::
+       :widths: 30 30
+       :header-rows: 1
+
+       * - action
+         - description
+       * - ``migration``
+         - .. watcher-term:: watcher.applier.actions.migration.Migrate
+       * - ``change_nova_service_state``
+         - .. watcher-term:: watcher.applier.actions.change_nova_service_state.ChangeNovaServiceState
+
+Planner
+*******
+
+Default Watcher's planner:
+
+    .. watcher-term:: watcher.decision_engine.planner.default.DefaultPlanner
+
+Configuration
+-------------
+
+Strategy parameter is:
+
+====================== ====== ============= ===================================
+parameter              type   default Value description
+====================== ====== ============= ===================================
+``migration_attempts`` Number 0             Maximum number of combinations to
+                                            be tried by the strategy while
+                                            searching for potential candidates.
+                                            To remove the limit, set it to 0
+====================== ====== ============= ===================================
+
+Efficacy Indicator
+------------------
+
+.. watcher-func::
+  :format: literal_block
+
+  watcher.decision_engine.goal.efficacy.specs.ServerConsolidation.get_global_efficacy_indicator
+
+How to use it ?
+---------------
+
+.. code-block:: shell
+
+    $ openstack optimize audittemplate create \
+      at1 server_consolidation --strategy basic
+
+    $ openstack optimize audit create -a at1 -p migration_attempts=4
+
+External Links
+--------------
+None.