correct port

Author: jsta

README.md

@@ -8,7 +8,7 @@
 ## Contributing to lesson development
 
 - The lesson files to be edited are in the `_episodes` folder. This repository uses the `main` branch for development.
-- You can visualize the changes locally with the [sandpaper](https://github.com/carpentries/sandpaper) R package by executing either the `sandpaper::serve()` or `sandpaper::build_lesson()` commands. In the former case, the site will be rendered at [http://localhost:4000](http://localhost:4000)
+- You can visualize the changes locally with the [sandpaper](https://github.com/carpentries/sandpaper) R package by executing either the `sandpaper::serve()` or `sandpaper::build_lesson()` commands. In the former case, the site will be rendered at [http://localhost:4321](http://localhost:4321)
 - Each time you push a change to GitHub, Github Actions rebuilds the lesson, and when it's successful (look for the green badge at the top of the README file), it publishes the result at [http://www.datacarpentry.org/r-raster-vector-geospatial/](http://www.datacarpentry.org/r-raster-vector-geospatial/)
 - Note: any manual commit to `gh-pages` will be erased and lost during the automated build and deploy cycle operated by Github Actions.