Recommend using bundle for running docs locally

Created by: hkdobrev

Closes https://github.com/twbs/bootstrap/issues/17493

Continuing from #17227.

docs/getting-started/build-tools.md

@@ -13,7 +13,8 @@ To use our Gruntfile and run our documentation locally, you'll need a copy of Bo
 1. [Download and install Node](https://nodejs.org/download), which we use to manage our dependencies.
 2. Install the Grunt command line tools, `grunt-cli`, with `npm install -g grunt-cli`.
 3. Navigate to the root `/bootstrap` directory and run `npm install` to install our local dependencies listed in [package.json](https://github.com/twbs/bootstrap/blob/master/package.json).
-4. [Install Ruby][install-ruby], install [Bundler][gembundler] with `gem install bundler`, and finally run `bundle`. This will install all Ruby dependencies, such as Jekyll and Sass linter.
+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 unofficial guide](http://jekyll-windows.juthilo.com/) to get Jekyll up and running without problems.
 
 When completed, you'll be able to run the various Grunt commands provided from the command line.
 
@@ -50,9 +51,8 @@ For example, run `TWBS_SASS=sass grunt` to test and build Bootstrap with Ruby Sa
 
 Running our documentation locally requires the use of Jekyll, a decently flexible static site generator that provides us basic includes, Markdown-based files, templates, and more. Here's how to get it started:
 
-1. Run through the [tooling setup](#tooling-setup) above to install Jekyll (the site builder) and Rouge (our syntax highlighter).
-  - **Windows users:** Read [this unofficial guide](http://jekyll-windows.juthilo.com/) to get Jekyll up and running without problems.
-2. From the root `/bootstrap` directory, run `jekyll serve` in the command line.
+1. Run through the [tooling setup](#tooling-setup) above to install Jekyll (the site builder) and other Ruby dependencies with `bundle install`.
+2. From the root `/bootstrap` directory, run `bundle exec jekyll serve` in the command line.
 3. Open <http://localhost:9001> in your browser, and voilà.
 
 Learn more about using Jekyll by reading its [documentation](http://jekyllrb.com/docs/home/).

README.md

@@ -66,11 +66,9 @@ Bootstrap's documentation, included in this repo in the root directory, is built
 
 ### Running documentation locally
 
-1. If necessary, [install Jekyll](http://jekyllrb.com/docs/installation) (requires v2.5.x).
-  - **Windows users:** Read [this unofficial guide](http://jekyll-windows.juthilo.com/) to get Jekyll up and running without problems.
-2. Install the Ruby-based syntax highlighter, [Rouge](https://github.com/jneen/rouge), with `gem install rouge`.
-3. From the root `/bootstrap` directory, run `jekyll serve` in the command line.
-4. Open <http://localhost:9001> in your browser, and voilà.
+1. Run through the [tooling setup](https://github.com/twbs/bootstrap/blob/master/docs/getting-started/build-tools#tooling-setup) to install Jekyll (the site builder) and other Ruby dependencies with `bundle install`.
+2. From the root `/bootstrap` directory, run `bundle exec jekyll serve` in the command line.
+3. Open <http://localhost:9001> in your browser, and voilà.
 
 Learn more about using Jekyll by reading its [documentation](http://jekyllrb.com/docs/home/).