feat: add Discord back, part 1

Author: NoaHimesaka1873

mkdocs.yml

@@ -130,5 +130,7 @@ extra:
     social:
         - icon: simple/matrix
           link: https://matrix.to/#/#space:t2linux.org
+        - icon: fontawesome/brands/discord
+          link: https://discord.com/invite/68MRhQu
         - icon: fontawesome/brands/github
           link: https://github.com/t2linux