docs: merge v4 and v5 readmes

Author: serhalp

README.md

@@ -1,6 +1,6 @@
-![Next.js Runtime](https://github.com/netlify/next-runtime/raw/main/next-js-runtime.png)
+![Next.js Runtime](next-js-runtime.png)
 
-# `@netlify/plugin-nextjs`
+# Next.js Runtime
 
 <p align="center">
   <a aria-label="npm version" href="https://www.npmjs.com/package/@netlify/plugin-nextjs">
@@ -16,3 +16,63 @@ Netlify. You should not normally need to install it yourself, as it is used auto
 builds of Next.js sites. See
 [the docs for using Next.js on Netlify](https://docs.netlify.com/frameworks/next-js/overview/) for
 more details.
+
+Next.js is supported natively on Netlify, and in most cases you will not need to install or
+configure anything. This repo includes the packages used to support Next.js on Netlify.
+
+## Prerequisites
+
+- Next.js 13.5 or later
+- Node.js 18 or later
+- The latest version of the [Netlify CLI](https://docs.netlify.com/cli/get-started/)
+
+## Deploying
+
+If you build on Netlify, the Next.js Runtime will work with no additional configuration.
+
+## Manually installing the Next.js Runtime
+
+The Next.js Runtime installs automatically for new Next.js sites on Netlify. You can also install it
+manually in the following ways:
+
+### From the UI (Recommended)
+
+You can go to the [UI](https://app.netlify.com/plugins/@netlify/plugin-nextjs/install) and choose
+the site to install the Next.js Runtime on. This method is recommended because you will benefit from
+auto-upgrades to important fixes and feature updates.
+
+### From `npm`
+
+```shell
+npm install -D @netlify/plugin-nextjs
+```
+
+...then add the following to your `netlify.toml` file:
+
+```toml
+[[plugins]]
+  package = "@netlify/plugin-nextjs"
+```
+
+This method is recommended if you wish to pin the Next.js Runtime to a specific version.
+
+## v4
+
+If you are using Next.js 10-13.4 or Node.js < 18, you must use v4 of the Next.js Runtime.
+
+If you are still using v4, you can find
+[its README here](https://github.com/netlify/next-runtime/blob/v4/README.md) and the
+[v4 Runtime docs here](https://docs.netlify.com/frameworks/next-js/runtime-v4/overview/).
+
+### Upgrading from v4 to v5
+
+To upgrade from v4 to v5, please visit
+[the v5 documentation](https://docs.netlify.com/frameworks/next-js/overview/).
+
+## Feedback
+
+If you think you have found a bug in Next.js on Netlify,
+[please open an issue](https://github.com/netlify/next-runtime/issues). If you have comments or
+feature requests, [see the discussion board](https://github.com/netlify/next-runtime/discussions)
+
+Please note that v4 will only receive security fixes and critical bug fixes.