Add auto updating last modified code to blog posts

remark-modified-time.mjs

@@ -0,0 +1,9 @@
+import { execSync } from "node:child_process";
+
+export function remarkModifiedTime() {
+  return (tree, file) => {
+    const filepath = file.history[0];
+    const result = execSync(`git log -1 --pretty="format:%cI" "${filepath}"`);
+    file.data.astro.frontmatter.lastModified = result.toString();
+  };
+}