Add a header comment to devsite md files. (#5865)

* Add a header comment to devsite md files.

* formatting

Author: hsubox76

scripts/docgen/docgen.ts

@@ -20,8 +20,21 @@ import { mapWorkspaceToPackages } from '../release/utils/workspace';
 import { projectRoot } from '../utils';
 import fs from 'fs';
 import glob from 'glob';
+import { join } from 'path';
 import * as yargs from 'yargs';
 
+/**
+ * Add to devsite files to alert anyone trying to make a documentation fix
+ * to the generated files.
+ */
+const GOOGLE3_HEADER = `{% comment %}
+DO NOT EDIT THIS FILE!
+This is generated by the JS SDK team, and any local changes will be
+overwritten. Changes should be made in the source code at
+https://github.com/firebase/firebase-js-sdk
+{% endcomment %}
+`;
+
 const tmpDir = `${projectRoot}/temp`;
 
 yargs
@@ -101,6 +114,15 @@ async function generateDocs(forDevsite: boolean = false) {
     { stdio: 'inherit' }
   );
 
+  if (forDevsite) {
+    const mdFiles = fs.readdirSync(join(projectRoot, outputFolder));
+    for (const mdFile of mdFiles) {
+      const fullPath = join(projectRoot, outputFolder, mdFile);
+      const content = fs.readFileSync(fullPath, 'utf-8');
+      fs.writeFileSync(fullPath, GOOGLE3_HEADER + content);
+    }
+  }
+
   moveRulesUnitTestingDocs(outputFolder, command);
 }