It's definitely possible to add new fonts for Studio, though you won't add them via the Studio app itself. Instead, you'll need to install new fonts in your system library and ensure that they are enabled for use with apps. The steps for installing fonts differ based on whether you're using a Mac or a Windows device.
Installing fonts on a Mac
To install fonts on your Mac:
Download the font or font family.
In Finder, double-click the font file/s.
In the dialog that opens, click Install Font.
Your Mac will validate the font and open it in Font Book.
In the All Fonts tab of Font Book, ensure the new font is enabled—i.e., it should not appear dimmed or grayed out.
After completing the steps above, close Studio completely. When you re-open Studio and select a text layer, you should see the new font available in the Inspector panel.