Remove sdc module from readme instructions

[hkirsman]

Our readme says that we needs sdc contrib module

wunder-theme-base/README.md

Line 10 in 79d1ec5

composer require drupal/sdc drupal/storybook drupal/twig_field_value drupal/twig_tweak

Drupal docs says otherwise https://www.drupal.org/docs/develop/theming-drupal/using-single-directory-components

Also the sdc module page says https://www.drupal.org/project/sdc

If this would be composer package, we could add Drupal and contrib requirements in composer.json. I'll start another ticket for that here #11

[Outim]

I have created a PR for this and for the issue #13: #15