fix: add UI-based install back in

Author: jlengstorf

CHANGELOG.md

@@ -14,8 +14,8 @@ If you've installed this plugin via Netlify's UI, no action is necessary. The up
 
 If you've installed this plugin manually in your `netlify.toml`, you can upgrade two ways:
 
-1. Use the new automatic install! Remove this plugin from your project and `netlify.toml` and Netlify will automatically install it for a seamless experience working with Next.js on Netlify.
-2. Manually update to the latest version using `npm i @netlify/plugin-nextjs@latest`.
+1. Manually update to the latest version using `npm i @netlify/plugin-nextjs@latest`.
+2. If you prefer to automatically get updates, remove this plugin from your project and `netlify.toml`, then [install the plugin using the Netlify UI](http://app.netlify.com/plugins/@netlify/plugin-nextjs/install).
 
 ## 2.0.1 (2021-02-17)
 

README.md

@@ -26,12 +26,18 @@ This build plugin is a utility for supporting Next.js on Netlify. To enable serv
 
 ## Installation and Configuration
 
+### For new Next.js sites
+
 As of v3.0.0, all new sites deployed to Netlify with Next.js will automatically install this plugin for a seamless experience deploying Next.js on Netlify!
 
 This means that you don't have to do anything — just build and deploy your site to Netlify as usual and we'll handle the rest.
 
 You're able to [remove the plugin](https://docs.netlify.com/configure-builds/build-plugins/#remove-a-plugin) at any time by visiting the **Plugins** tab for your site in the Netlify UI.
 
+### UI-based installation for existing Next.js sites
+
+If your Next.js project is already deployed to Netlify, use the Netlify UI to [install the Essential Next.js Build Plugin](http://app.netlify.com/plugins/@netlify/plugin-nextjs/install) in a few clicks.
+
 ### Manual installation
 
 1\. Create a `netlify.toml` in the root of your project. Your file should include the plugins section below: