Add Open Graph logo meta tag

Add an og:logo meta tag in src/layouts/main.astro pointing to the SCI logo (https://web-sci.greensoftware.foundation/assets/sci-logo.svg) so social previews (Open Graph/Facebook) can include the site logo.

Author: russelltrow

src/layouts/main.astro

@@ -49,6 +49,7 @@ import "../styles/global.css";
 
     <!-- Open Graph / Facebook -->
     <meta property="og:type" content="website" />
+    <meta property="og:logo" content="https://web-sci.greensoftware.foundation/assets/sci-logo.svg" />
     <meta property="og:url" content="https://web-sci.greensoftware.foundation/" />
     <meta
       property="og:title"