web: allow markdown import

Signed-off-by: Jens Langhammer <jens.langhammer@beryju.org>

web/src/global.d.ts

@@ -1,4 +1,9 @@
 declare module "*.css";
+declare module "*.md" {
+    const html: string;
+    const metadata: object;
+    const filename: string;
+}
 
 declare namespace Intl {
     class ListFormat {