Extract developer site (#5249)

* Extract developer site

* Fix title in sidebar

* Update dev section reference

* Update edit in github link on help page

source/developers/development.markdown

@@ -9,23 +9,6 @@ sharing: true
 footer: true
 ---
 
-Home Assistant is built from the ground up to be easily extensible using components. Home Assistant uses [Python 3](https://www.python.org/) for the backend and [Polymer (Web components)](https://www.polymer-project.org/) for the frontend.
-
-Home Assistant is open-source and licensed under [Apache 2.0](http://www.apache.org/licenses/LICENSE-2.0). Here are links to the source:
-
- - [home-assistant](https://github.com/home-assistant/home-assistant): Python server backend.
- - [home-assistant-polymer](https://github.com/home-assistant/home-assistant-polymer): Polymer UI.
-
-For those new to contributing to open source software, make sure you are familiar with all of the tools and concepts used in Home Assistant before you start. 
-
-When contributing Home Assistant code:
- - [Github](https://guides.github.com/activities/hello-world/)
- - [Pip and Virtual Environments](https://www.dabapps.com/blog/introduction-to-pip-and-virtualenv-python/)
- - [Python 3](https://www.python.org/)
- - [Pylint](https://www.pylint.org)
- - [Flake8](http://flake8.pycqa.org/en/latest/)
- - [Tox](http://tox.readthedocs.org/en/latest/)
- - [TravisCl](https://travis-ci.org/)
-
-When contributing 3rd Party code to be used by Home Assistant:
- - [Publishing your own PyPI package](https://jeffknupp.com/blog/2013/08/16/open-sourcing-a-python-project-the-right-way/)
+<script>
+window.location = 'https://developers.home-assistant.io/docs/en/development_index.html';
+</script>