message: Update sketchfab help text
diff: <app-form-group
  name="sketchfab_id"
  hide-label
  - :label="$gettext(`Sketchfab Model ID`)"
  + :label="$gettext(`Sketchfab Model URL`)"
  v-app-focus-when="!wasPublished"
  >
  <p class="help-block">
  - <translate>Enter the ID in your Sketchfab model's URL. For example:</translate>
  + <translate>Enter your Sketchfab model's URL. For example:</translate>
  <code>
  - https://sketchfab.com/3d-models/your-model-name-
  - <strong>ID</strong>
  + https://sketchfab.com/3d-models/your-model-name-ID
  </code>
  </p>
  