Add a docs site build version indicator in the footer. (#37)

gatsby-node.ts

@@ -1,7 +1,9 @@
 import createPages from './src/gatsby/createPages';
 import onCreateNode from './src/gatsby/onCreateNode';
+import onPreBuild from './src/gatsby/onPreBuild';
 
 module.exports = {
   createPages,
   onCreateNode,
+  onPreBuild,
 };

src/components/Footer.tsx

@@ -19,7 +19,8 @@ export const Footer: React.FC = () => {
             </ul>
           </nav>
         )}
-        <span>© 2023 All rights reserved zk Foundation</span>
+        <span>© 2024 All rights reserved zk Foundation</span>
+        <span style={{fontSize: "0.85em"}}>Build {process.env.GATSBY_GIT_SHA}↦{process.env.GATSBY_BUILD_DATE}</span>
       </div>
     </footer>
   );

src/components/layout/Layout.tsx

@@ -55,6 +55,8 @@ export const Head = ({ pageContext }: PageNode) => {
       <meta name="twitter:card" content="summary_large_image" />
       <meta name="twitter:site" content={config.twitterName} />
       <meta name="og:site_name" content={config.title} />
+      <meta name="publish-date" content={process.env.GATSBY_BUILD_DATE} />
+      <meta name="version" content={process.env.GATSBY_GIT_SHA} />
     </>
   );
 };

src/gatsby/onPreBuild.ts

@@ -0,0 +1,8 @@
+import { execSync } from 'child_process';
+
+const onPreBuild = async () => {
+  process.env.GATSBY_BUILD_DATE = new Date().toISOString();
+  process.env.GATSBY_GIT_SHA = execSync('git rev-parse HEAD').toString().trim().substring(0,8);
+};
+
+export default onPreBuild;