Update UI Suite Bootstrap Starterkit README.md to add example command for dr

Problem/Motivation

The UI Suite Bootstrap Starterkit README.md and UI Suite Bootstrap Starterkit Split README.md provide the following example command to generate a theme using the starterkit: php core/scripts/drupal generate-theme my_theme --starterkit ui_suite_bootstrap_starterkit --path themes/custom

Starting in Drupal 11.4.0, this results in an error message because WEBROOT/core/scripts/drupal is deprecated and replaced with WEBROOT/core/scripts/dr (source: dr - Drupal CLI capable of running commands from modules).

Steps to reproduce

Install Drupal core 11.4+, UI Suite Bootstrap 5.2+, and any related dependencies.

Run the example command in the UI Suite Bootstrap Starterkit README.md (php core/scripts/drupal generate-theme my_theme --starterkit ui_suite_bootstrap_starterkit --path themes/custom). Edit the command for your system, if needed, such as beginning with ddev and adding web/ before core if web is your webroot.

Result: Long error message that begins with PHP Deprecated: Calling drupal is deprecated in drupal:11.4.0 and is removed from drupal:13.0.0. Use the `dr` script instead. See https://www.drupal.org/node/3584928 in /var/www/html/web/core/scripts/drupal on line 16, followed by several deprecation and warning messages and stack traces, and ending with Failed to run php web/core/scripts/drupal generate-theme my_theme --starterkit ui_suite_bootstrap_starterkit --path themes/custom: exit status 255.

Proposed resolution

Update UI Suite Bootstrap Starterkit README.md and UI Suite Bootstrap Starterkit Split README.md to add an example command for using dr.

Proposed new wording in "Usage" section of README.md files:

Example command to generate your theme in Drupal 10.3+ - 11.3:
php core/scripts/drupal generate-theme my_theme --starterkit ui_suite_bootstrap_starterkit --path themes/custom
Note: If you are using web (or docroot) as the webroot add the webroot at the beginning of the script path. Example: web/core/scripts/drupal.

Example command to generate your theme in Drupal 11.4+:
exec vendor/bin/dr generate-theme my_theme --starterkit ui_suite_bootstrap_starterkit --path themes/custom

In both examples, preface the command with the appropriate command for your development environment. Example if using DDEV: ddev exec vendor/bin/dr generate-theme my_theme --starterkit ui_suite_bootstrap_starterkit --path themes/custom.

Remaining tasks

Create MR.
Review.
Merge.
Commit.
Credit @yannickoo who provided the revised command for use with dr in this conversation in Slack.

User interface changes

None

API changes

None

Data model changes

None