connect to links and open in new tabs

[EmmaBin]

Ticket Description

• [x] Documentation button should link to https://docs.specollective.org/introduction/
• [x] Donate button should link to https://opencollective.com/spec
• [x] Outside links should open in a new tab

Description of Changes

changed Navbar.tsx file

Before and After for UI Updates

Before:

After:

For PR Reviewer

• [x] Does this file change the yarn.lock, package.json or package-lock.json file? If so, why?
• [x] If this pr contains mobile and desktop changes, did you test on IphoneXr and desktop views?
• [x] Does this file match the related tickets linked figma file, or does it pass the visual smell test?
• [x] If this file contains javascript, does the javascript pass the smell test?
• [x] If you don't feel super confident in your review, did you assign someone more senior to double check?