docs: Add OpenCollective link and donate button

docs/index.mdx

@@ -15,6 +15,9 @@ hero:
     - theme: alt
       text: Star on GitHub
       link: https://github.com/continuwuity/continuwuity
+    - theme: alt
+      text: Donate to us!
+      link: https://opencollective.com/continuwuity
   image:
     src: /assets/logo.svg
     alt: continuwuity logo

rspress.config.ts

@@ -52,6 +52,13 @@ export default defineConfig({
                 mode: 'link',
                 content: 'https://github.com/continuwuity/continuwuity',
             },
+            {
+                icon: {
+                    svg: `<svg role="img" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><title>Open Collective</title><path fill="currentColor" d="M12 0C5.373 0 0 5.373 0 12s5.373 12 12 12c2.54 0 4.894-.79 6.834-2.135l-3.107-3.109a7.715 7.715 0 1 1 0-13.512l3.107-3.109A11.943 11.943 0 0 0 12 0zm9.865 5.166l-3.109 3.107A7.67 7.67 0 0 1 19.715 12a7.682 7.682 0 0 1-.959 3.727l3.109 3.107A11.943 11.943 0 0 0 24 12c0-2.54-.79-4.894-2.135-6.834z"/></svg>`
+                },
+                mode: 'link',
+                content: 'https://opencollective.com/continuwuity',
+            },
         ],
         lastUpdated: true,
         enableContentAnimation: true,