Implement Giscus (#503)

* add giscus

* fix lint

* prettify

Co-authored-by: Dimitri POSTOLOV <dmytropostolov@gmail.com>

packages/web/docs/theme.config.tsx

@@ -1,7 +1,28 @@
 /* eslint sort-keys: error */
-import { defineConfig } from '@theguild/components';
+import { defineConfig, useTheme, Giscus } from '@theguild/components';
+import { useRouter } from 'next/router';
 
 export default defineConfig({
   docsRepositoryBase: 'https://github.com/kamilkisiela/graphql-hive/tree/main/packages/web/docs',
+  main({ children }) {
+    const { resolvedTheme } = useTheme();
+    const { route } = useRouter();
+
+    return (
+      <>
+        {children}
+        <Giscus
+          // ensure giscus is reloaded when client side route is changed
+          key={route}
+          repo="kamilkisiela/graphql-hive"
+          repoId="R_kgDOHWr5kA"
+          category="Docs Discussions"
+          categoryId="DIC_kwDOHWr5kM4CSDSS"
+          mapping="pathname"
+          theme={resolvedTheme}
+        />
+      </>
+    );
+  },
   siteName: 'HIVE',
 });