Refactored the doc subtree

We need to start working on some introductory materials for the project
and service. We may also need to document our thoughts and design
decisions when moving forward. This patch tries to provide a basic
layout of the documents.

Change-Id: Iad4affead02d605c6fce2720adc85141fd1dc419

doc/source/developer/profile_type.rst

@@ -0,0 +1,35 @@
+..
+  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.
+
+
+Development Guide for Profile Types
+===================================
+
+Implementation Hints
+--------------------
+
+Handling Context
+^^^^^^^^^^^^^^^^
+
+In the Profile class implementation, a profile can be stored into DB and then
+loaded from DB given an ID. We don't record the context used by a profile. On
+the contrary, the context is assigned to a profile when it is (re)intialized.
+This enables a profile to be used by different context, which is usually the
+context saved into an action. There won't be security problem if we have
+recorded the correct context of an action.
+
+Abstract Methods
+^^^^^^^^^^^^^^^^
+
+The Profile class provides abstract methods such as `do_create()`,
+`do_delete()` and `do_update()` for sub-classes to override.