docs(build tools): mention how to get the sources (#31589)

site/docs/4.5/getting-started/build-tools.md

@@ -13,8 +13,9 @@ Bootstrap uses [npm scripts](https://docs.npmjs.com/misc/scripts) for its build
 To use our build system and run our documentation locally, you'll need a copy of Bootstrap's source files and Node. Follow these steps and you should be ready to rock:
 
 1. [Download and install Node.js](https://nodejs.org/en/download/), which we use to manage our dependencies.
-2. Navigate to the root `/bootstrap` directory and run `npm install` to install our local dependencies listed in [package.json]({{ site.repo }}/blob/v{{ site.current_version }}/package.json).
-3. [Install Ruby][install-ruby], install [Bundler][gembundler] with `gem install bundler`, and finally run `bundle install`. This will install all Ruby dependencies, such as Jekyll and plugins.
+2. Either [download Bootstrap's sources]({{ site.download.source }}) or fork [Bootstrap's repository]({{ site.repo }}).
+3. Navigate to the root `/bootstrap` directory and run `npm install` to install our local dependencies listed in [package.json]({{ site.repo }}/blob/v{{ site.current_version }}/package.json).
+4. [Install Ruby][install-ruby], install [Bundler][gembundler] with `gem install bundler`, and finally run `bundle install`. This will install all Ruby dependencies, such as Jekyll and plugins.
   - **Windows users:** Read [this guide](https://jekyllrb.com/docs/windows/) to get Jekyll up and running without problems.
 
 When completed, you'll be able to run the various commands provided from the command line.