Add installation instructions to readme

Author: marijnh

README.md

@@ -5,12 +5,6 @@
 [![Join the chat at https://gitter.im/codemirror/CodeMirror](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/codemirror/CodeMirror)  
 [Funding status: ![maintainer happiness](https://marijnhaverbeke.nl/fund/status_s.png?again)](https://marijnhaverbeke.nl/fund/)
 
-**NOTE**: This is the source repository for the library, and not the
-distribution channel. You need to run a build step if you want to use
-this code. To install the software pre-built, get it from
-[NPM](https://www.npmjs.com/package/codemirror) or [the
-website](https://codemirror.net/codemirror.zip).
-
 CodeMirror is a versatile text editor implemented in JavaScript for
 the browser. It is specialized for editing code, and comes with over
 100 language modes and various addons that implement more advanced
@@ -35,6 +29,19 @@ The CodeMirror community aims to be welcoming to everybody. We use the
 (1.1)](http://contributor-covenant.org/version/1/1/0/) as our code of
 conduct.
 
+### Installation
+
+Either get the [zip file](https://codemirror.net/codemirror.zip) with
+the latest version, or make sure you have [Node](https://nodejs.org/)
+installed and run:
+
+    npm install codemirror
+
+**NOTE**: This is the source repository for the library, and not the
+distribution channel. Cloning it is not the recommended way to install
+the library, and will in fact not work unless you also run the build
+step.
+
 ### Quickstart
 
 To build the project, make sure you have Node.js installed (at least version 6)