Bring back indicator documentation with a note that the feature has b…

…een removed

docs/api-reference/next.config.js/static-optimization-indicator.md

@@ -0,0 +1,21 @@
+---
+description: Optimized pages include an indicator to let you know if it's being statically optimized. You can opt-out of it here.
+---
+
+# Static Optimization Indicator
+
+> **Note:** This indicator was removed in Next.js version 10.0.1. We recommend upgrading to the latest version of Next.js.
+
+When a page qualifies for [Automatic Static Optimization](/docs/advanced-features/automatic-static-optimization.md) we show an indicator to let you know.
+
+This is helpful since automatic static optimization can be very beneficial and knowing immediately in development if the page qualifies can be useful.
+
+In some cases this indicator might not be useful, like when working on electron applications. To remove it open `next.config.js` and disable the `autoPrerender` config in `devIndicators`:
+
+```js
+module.exports = {
+  devIndicators: {
+    autoPrerender: false,
+  },
+}
+```