Add outline / rough draft of new Overview page (pypa#519)

* adding mostly-skeleton overview

* draft talk about frameworks/platforms

* expand a little on each section

* address most of @ncoghlan's initial review points at pypa#519

* fix @pradyunsg's very valuable copyedits

* update title for searchability, add a bit to the binary distribution section, all per @theacodes comments

* flesh out sections, clarify zipapp qualification, add a few links

* expand image sections, add a few related links

* refining a lot of phrasing, expanding on hardware, adding figures

* lots of links, and expand on considerations (i think wheels might be the only thing left)

* link freezers

* more links, slight tweaks to the intro and other language, provide a linked summary of wheels

* link to overview from home page

* various rephrasals and addition of a couple asides

* fix typo

* address most copyediting concerns, tweak a header, and add thea's expansion of the modules section.

* try to tie sdists and wheels more closely together as recommended practice

* new -> separate, add a bit more detail

* improve frameworks section intro

* add additional encouragement to dual-publish wheels and sdists

* adjust heading consistency and add notes for future editors

* a few tweaks for flow, plus a favorite quote from Wikipedia for the editors' notes

* add link to jupyterlab writing advice

Author: mahmoud

source/assets/py_pkg_applications.png

@@ -6,6 +6,7 @@ Python Packaging User Guide
    :maxdepth: 2
    :hidden:
 
+   overview
    tutorials/index
    guides/index
    discussions/index
@@ -32,8 +33,10 @@ happily accept any :doc:`contributions and feedback <contribute>`. 😊
 Get started
 ===========
 
-Essential tools and concepts for working with the Python packaging ecosystem are
-covered in our :doc:`tutorials/index` section:
+Thinking about shipping a new Python library or application? Start with :doc:`overview`.
+
+Essential tools and concepts for working within the Python
+development ecosystem are covered in our :doc:`tutorials/index` section:
 
 * to learn how to install packages, see the
   :doc:`tutorial on installing packages <tutorials/installing-packages>`.