Add more explanation to README.md

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Author: gtback

README.md

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 # python-cybox [![Build Status](https://travis-ci.org/CybOXProject/python-cybox.png)](https://travis-ci.org/CybOXProject/python-cybox)
 
-A python library for parsing, manipulating, and generating CybOX content.
-
-This currently consists of only the XML-to-Python bindings files, but in the
-future will contain many helper utilities and a more intuitive API.
+A Python library for parsing, manipulating, and generating CybOX content.
 
 For more information about CybOX, see http://cybox.mitre.org.
 
 
+## Overview
+
+A primary goal of the python-cybox library is to remain faithful to both the
+CybOX standard and to customary Python practices. There are places where these
+will conflict, and the goal is to make the library intuitive both to those
+familiar with the XML schemas (but less familiar with Python) and also to
+experienced Python developers who want to add CybOX support to their programs.
+
+There are currently two levels of APIs for dealing with CybOX content:
+
+- A low-level API is provided by auto-generated XML Schema - Python class
+  bindings. These bindings were generated using
+  [generateDS](http://www.rexx.com/~dkuhlman/generateDS.html). With these,
+  any CybOX content can be parsed from or written to XML, but requires a bit
+  more knowledge of the actual CybOX schemas. These "binding classes" are all
+  located in the `cybox.bindings` package.
+- A higher-level API consisting of manually designed Python classes. These
+  "native classes" are intended to behave more like Python programmers would
+  expect. As they are designed manually, they currently do not support the
+  entire CybOX standard, but rather those object types we expect are used most
+  frequently. These "native classes" also support exporting their content as
+  Python dictionaries and lists, which can easily be converted to JSON.
+  Importing from JSON is also supported.
+
+Note: Due to the release of Version 2.0 of the CybOX Language, the full set of
+"native classes" will most likely never be complete for Version 1.0. If you are
+developing an application which MUST use Version 1.0 of the CybOX Language,
+please contact us (see below) so we can try to meet your needs.
+
+
+## Versioning
+
+Releases of the python-cybox library will be given `major.minor.revision`
+version numbers, where `major` and `minor` correspond to the CybOX version
+being supported. The `revision` number is used to indicate new versions of
+the Python library itself.
+
+
 ## Installation
 
-The 'cybox' package depends on the 'lxml' XML parsing library.
+The `cybox` package depends on the `lxml` XML parsing library.
 
 To build `lxml` on Ubuntu, you will need the following packages from the
 Ubuntu package repository:
@@ -21,3 +56,10 @@ Ubuntu package repository:
 
 For more information about installing lxml, see
 http://lxml.de/installation.html
+
+
+## Feedback
+
+Bug reports and feature requests are welcome and encouraged. Pull requests are
+especially appreciated. Feel free to use the issue tracker on GitHub or send
+an email directly to [email protected].