How can I link css/js from main bootstrap theme to subtheme?
The fact that you've got the Drupal Bootstrap site logo means the theme was correctly enabled. However, this is a symptom of the browser not finding your CSS file.

And you don't actually use the Bootstrap CSS that comes with the parent theme. You actually have to import Bootstrap into your SASS/LESS. That's why you need to download Bootstrap to your subtheme (Step 4).

If you're using the SASS/LESS starterkit, you will actually need to compile your CSS (that's steps 4 and 5 of the Overview). Once you've got it compiling, you need to tell your subtheme the path of the compiled CSS by adding it to the info file (step 3 of the Overview).

stylesheets[all][] = path/to/compiled/styles.css