[projects] Add project: Typst Extra Docs (#306)

Co-authored-by: YDX-2147483647 <73375426+YDX-2147483647@users.noreply.github.com>

Author: github-actions[bot]

projects.yaml

@@ -1549,3 +1549,8 @@ projects:
     github_id: sumsupee/cursorfortypst
     category: writing
     labels: [web]
+
+  - name: Typst Extra Docs
+    github_id: typst-community/extra-docs
+    category: docs
+    labels: [web]