Add archival note to README as well

Author: takluyver

README.md

@@ -3,7 +3,36 @@
 This is the main website for a pledge to stop supporting Python 2 for free in
 open source software.
 
-# Run locally
+## History
+
+This page is now an archive of part of the transition from Python 2 to 3.
+
+By around 2015, when Python 2 support was originally planned to end, many
+important Python libraries and tools supported Python 3. But Python 2 still had
+a lot of users, and projects needed to support both major versions. The end of
+Python 2 support was postponed to 2020, and some people argued that development
+of Python 2 should resume. It seemed like a real possibility that the end date
+would be postponed again, and we'd need to support two versions of the language
+indefinitely.
+
+The Python 3 statement was drawn up around 2016. Projects pledged to require
+Python 3 by 2020, giving other projects confidence that they could plan a similar
+transition, and allowing downstream users to figure out their options without a
+nasty surprise. We didn't force people to move to Python 3, but if they wanted
+to stick with Python 2, they would stop getting new versions of our projects.
+The focus was originally on the scientific Python ecosystem, with Jupyter and
+matplotlib among the first projects involved, but in late 2017 it was expanded
+to any Python projects.
+A rapidly growing number of projects signed up as we approached 2020.
+
+The long-term transition we hoped for has succeeded: in 2024 it is entirely
+normal for projects to support only Python 3, simplifying maintainers' lives
+and letting us take full advantage of newer language features.
+
+Thank-you to all of the people, in projects big and small, who contributed
+their support to the statement!
+
+## Run locally
 
 Install Jekyll : `gem install jekyll`, `gem install github-pages`
 
@@ -15,7 +44,9 @@ Modify the various files, refresh your browser and enjoy.
 
 PRs welcomed.
 
-# Add your project
+## Add your project
+
+We're no longer adding new projects - see the history section above.
 
 If you just want to add your project to the list of participating projects, add
 a line in [the list of participating projects](_sections/30-projects.md). It's
@@ -25,7 +56,7 @@ online](https://github.com/python3statement/python3statement.github.io/edit/mast
 
 There is no need to install Jekyll: A check creating a preview will be run on your pull request. Please check this preview.
 
-## Add timeline information
+### Add timeline information
 
 The front page also has a timeline chart, with past release dates and future
 (planned) releases. You can also add your project there, if you have a specific
@@ -35,7 +66,7 @@ See [site.js](site.js) around [line
 100](https://github.com/python3statement/python3statement.github.io/blob/master/site.js#L103)
 to see how to add this kind of data.
 
-# Base template
+## Base template
 
 This site is based on
 [github.com/t413/SinglePaged](https://github.com/t413/SinglePaged).