Add welcome text and guides link to HPC landing page

Author: aswinnarayanan

sites/hpc/src/content/docs/index.mdx

@@ -4,5 +4,14 @@ description: Placeholder landing page for the UQ RCC HPC documentation site
 template: splash
 hero:
   title: UQ RCC HPC
-  tagline: Placeholder landing page
+  tagline: Welcome to the central index for information and guides for systems operated by the UQ Research Computing Centre.
+  actions:
+    - text: Browse the guides
+      link: /overview/
+      icon: open-book
+      variant: primary
 ---
+
+import { LinkCard } from '@astrojs/starlight/components';
+
+<LinkCard title="How to Acknowledge Bunya and/or RCC" href="https://rcc.uq.edu.au/about/acknowledging-rcc" />