docs: Add intro to extdev

docs/extensiondev.rst

@@ -8,6 +8,55 @@ Extension development
     development of Mopidy extensions should become in the future, not how to
     currently develop an extension for Mopidy.
 
+
+Mopidy started as simply an MPD server that could play music from Spotify.
+Early on Mopidy got multiple "frontends" to expose Mopidy to more than just MPD
+clients: for example the Last.fm frontend what scrobbles what you've listened
+to to your Last.fm account, the MPRIS frontend that integrates Mopidy into the
+Ubuntu Sound Menu, and the HTTP server and JavaScript player API making web
+based Mopidy clients possible. In Mopidy 0.9 we added support for multiple
+music sources without stopping and reconfiguring Mopidy: for example the local
+backend for playing music from your disk, the stream backend for playing
+Internet radio streams, and the Spotify and SoundCloud backends, for playing
+music directly from those services.
+
+All of these are examples of what you can accomplish by creating a Mopidy
+extension. If you want to create your own Mopidy extension for something that
+does not exist yet, this guide to extension development will help you get your
+extension running in no time, and make it feel the way users would expect your
+extension to behave.
+
+
+Anatomy of an extension
+=======================
+
+Extensions are all located in a Python package called ``mopidy_something``
+where "something" is the name of the application, library or web service you
+want to integrated with Mopidy. So for example if you plan to add support for a
+service named Soundspot to Mopidy, you would name your extension's Python
+package ``mopidy_soundspot``.
+
+The name of the actual extension (the human readable name) however would be
+something like "Mopidy-Soundspot". Make sure to include the name "Mopidy"
+somewhere in that name and that you check the capitalization. This is the name
+users will use when they install your extension from PyPI.
+
+The extension must be shipped with a ``setup.py`` file and be registered on
+`PyPI <https://pypi.python.org/>`_. Also make sure the development version link
+in your package details work so that people can easily install the development
+version into their virtualenv simply by running e.g. ``pip install
+Mopidy-Soundspot==dev``.
+
+Mopidy extensions must be licensed under an Apache 2.0 (like Mopidy itself),
+BSD, MIT or more liberal license to be able to be enlisted in the Mopidy
+Extension Registry. Keep in mind that the Mopidy Extension Registry is a
+moderated place and libraries will be reviewed upfront if they behave as
+required.
+
+
+Notes
+=====
+
 An extension wants to:
 
 - Be automatically found if installed