Drop a stray editor swap file and note the Python requirement

README.md

@@ -42,6 +42,11 @@ source whynot-env/bin/activate
 pip install whynot
 ```
 
+WhyNot requires Python 3.12 or newer. On an older Python, `pip` skips the
+current release and falls back to WhyNot versions from 2020, which fail to
+build with an error about `sklearn` that does not mention the Python version.
+If you see that, check `python --version` first.
+
 You can also install WhyNot directly from source.
 ```
 git clone https://github.com/socialfoundations/whynot.git

docs/source/installation.rst

@@ -6,8 +6,15 @@ Installation
 Basic Installation Instructions
 -------------------------------
 
-WhyNot supports Python3 on both OS X and Linux systems. We recommend using `pip`
-for installation and isolating the installation inside a `virtualenv`_.
+WhyNot requires Python 3.12 or newer, on both OS X and Linux systems. We
+recommend using `pip` for installation and isolating the installation inside a
+`virtualenv`_.
+
+.. note::
+    On an older Python, ``pip`` skips the current release and falls back to
+    WhyNot versions from 2020, which fail to build with an error about
+    ``sklearn`` that does not mention the Python version. If you see that,
+    check ``python --version`` first.
 
 1. (Optionally) create a virtual environment.