🔴 Fix broken og:image and dead CONTRIBUTING.md link

[drewferg11-hermes-bot]

Goal

Fix the two critical broken-link/asset issues found in the GitHub Pages site review that make the site look unfinished or broken to visitors and social platforms.

Issues found

1. 🔴 og:image returns 404 (broken social previews)

File: overrides/main.html

The override sets the Open Graph / Twitter Card image to:

{{ config.site_url }}assets/split-flap-display-banana.png

This resolves to https://drewferg11.github.io/Split-Flap-Display/assets/split-flap-display-banana.png → 404.

The actual file lives at assets/display/split-flap-display-banana.png (confirmed 200 OK).

Fix: Change the path in overrides/main.html to:

<meta property="og:image" content="{{ config.site_url }}assets/display/split-flap-display-banana.png">
<meta name="twitter:image" content="{{ config.site_url }}assets/display/split-flap-display-banana.png">

Every social share / Discord embed / Twitter card currently shows no preview image.

2. 🔴 Dead link in CONTRIBUTING.md to README#setup-instructions

File: CONTRIBUTING.md

The text says:

For build setup, see the Setup Instructions in the README.

The README has no "Setup Instructions" heading. Its headings are: # Split Flap Display, ## Flash Firmware, ## Features, ## Contributing, ## License. The link is dead.

Fix: Either add a ## Setup Instructions section to README.md (pointing to the firmware install docs), or change the link to https://drewferg11.github.io/Split-Flap-Display/firmware/install-manual/.

Acceptance criteria

• og:image and twitter:image meta tags resolve to a 200 OK URL
• Social share preview shows the split-flap-display-banana.png image
• CONTRIBUTING.md "Setup Instructions" link resolves to a real heading or external URL
• mkdocs build --strict passes

Files / areas involved

• overrides/main.html
• CONTRIBUTING.md
• README.md (if adding a Setup Instructions heading)

Constraints

• Don't change the og:image to a different image — just fix the path
• Keep the CONTRIBUTING.md link pointing to build/setup instructions, not somewhere unrelated