[microsite] Add redirect for /docs (#2101)

microsite/pages/en/docs.js

@@ -0,0 +1,12 @@
+const React = require('react');
+const Redirect = require('../../core/Redirect.js');
+
+const siteConfig = require(process.cwd() + '/siteConfig.js');
+
+function Docs() {
+  return (
+    <Redirect redirect="/docs/overview/what-is-backstage" config={siteConfig} />
+  );
+}
+
+module.exports = Docs;