Update README with new instructions

Author: lornajane

README.md

@@ -6,8 +6,24 @@ This repo holds the website content for https://rst2pdf.github.io.
 
 To contribute to this repo, make sure that your master branch is up to date and create a new branch from there.
 
-To run the project locally and check your work as you go along, try [these instructions from GitHub](https://help.github.com/articles/setting-up-your-github-pages-site-locally-with-jekyll/), which can be summarised as:
+The website content is in `source/`.
 
-    $ gem install bundler
-    $ bundle install
-    $ bundle exec jekyll serve
+### Develop locally
+
+This Python-based project uses [uv](https://docs.astral.sh/uv/) and [make](https://www.gnu.org/software/make/), so install those first if you don't have them already.
+
+1. Install dependencies
+
+   ```
+   uv sync
+   ```
+
+2. Build the site
+
+   ```
+   make html
+   ```
+
+   The output files are in the `build/` directory as HTML.
+
+3. (optional) Preview the files with `python -m http.server`.