You can add a link to your Facebook page on your Full Slate landing page by going to Setup > Company and adding it to the Description field. You might consider using the 'Create a link' button in the text editor in order to embed the link within your text.
You may also be able to add a "Like" button for your Facebook business page. To do this, go to https://developers.facebook.com/docs/reference/plugins/like/. Place your Facebook page domain (e.g. http://www.facebook.com/fullslate) in the "URL to like" field, choose your settings and click Get Code. Copy that code and go to Setup > Company in your Full Slate account. Locate the Description field and click the "Edit source" button (it has a little gear symbol) on the field's blue toolbar. Now paste your code into the box and click the gear button again.