[website] Add Discord link to nav links (#533)

Author: MysteryBlokHed

_includes/partials/_nav-links.njk

@@ -11,4 +11,5 @@
 <a href="https://elements.colorjs.io/">Elements</a>
 <a href="{{ page | relative }}/test/" class="footer">Tests</a>
 <a href="https://github.com/LeaVerou/color.js">GitHub</a>
+<a href="https://discord.gg/K64FJBznq4">Discord</a>
 <a href="https://github.com/LeaVerou/color.js/issues/new" class="footer">File bug</a>