Fix URLs fully with relative path helper

docs-src/_includes/relative-path.cjs

@@ -0,0 +1,9 @@
+const path = require('path').posix;
+
+module.exports = (base, p) => {
+  const relativePath = path.relative(base, p);
+  if (p.endsWith('/') && !relativePath.endsWith('/') && relativePath !== '') {
+    return relativePath + '/';
+  }
+  return relativePath;
+};