A more detailed gude for adding a board to CircuitPython can be found in the following Adafruit Learn guide: How to add a New Board to the circuitpython.org website

To add a new board to the site:

1. Duplicate template.md to _board/<board id>.md.
2. Edit _board/<board id>.md according to the template's instructions.
3. In your _board/<board id>.md you will specify a board_image. Create 3 versions of this file, in the following sizes and folder locations:

For more information on preferred images or if you prefer or must use 13:10 see Preparing the Images in the Adafruit Learn guide

4. Create a pull request with the file changes.

To test your changes locally:

1. You need "ruby" and "ruby-bundler" installed locally. These instructions were tested with ruby 2.5 and ruby-bundler 1.17.3 on a Debian Stretch system.
2. As needed, git submodule update --init --recursive to fetch the submodules
3. One time, run bundle config set path 'vendor/bundle' && bundle install
4. Run bundle exec jekyll serve to generate the site locally
5. Visit the displayed "server address"
6. After most local edits, the content will be updated. You will need to reload (ctrl-r or F5) your browser

Note: For faster jekyll builds, you can use the --incremental flag. You'll also want to install ruby with yjit enabled for even faster builds.