Add bootstrap -> bootstrap-vue migration notes

docs/SETUP.md

@@ -48,7 +48,7 @@ import {bAlert, bBtn} from 'bootstrap-vue/lib/components'
 <script src="//unpkg.com/bootstrap-vue@latest/dist/bootstrap-vue.js"></script>
 ```
 
-## Build variants 
+## Build variants
 Choosing the best variant for your build environment / packager helps less bundle sizes.
 If your bundler supports es modules, it will automatically prefer it over commonjs.
 
@@ -57,3 +57,10 @@ Variant        | Environments                 | Package path
 **ES Module**  | Webpack 2 / Rollup           | `dist/bootstrap-vue.esm.js`
 commonjs2      | Webpack 1 / ...              | `dist/bootstrap-vue.common.js`
 UMD            | Browser                      | `dist/bootstrap-vue.js`
+
+## Migrating a project already using Bootstrap
+If you've already been using Bootstrap 4, there are a couple adjustments you may need to make to your project:
+
+- remove the bootstrap.js file from your page scripts or build pipeline
+- if Bootstrap is the only thing relying on jQuery, you can safely remove it—bootstrap-vue **does not** depend on jQuery
+- don't forget to include the `bootstrap-vue.css` file!