docs: add theme colour (#5141)

sanjaiyan: theme color

Author: sanjaiyan-dev

packages/gatsby/src/components/seo.tsx

@@ -51,6 +51,10 @@ export function SEO({description, lang = `en`, meta = [], keywords = [], title}:
           name: `description`,
           content: metaDescription,
         },
+        {
+          name: `theme-color`,
+          content: `#25799f`,
+        },
         {
           property: `og:title`,
           content: title,