Add documentation regarding importing the module (#1768)

docs/node.md

@@ -2,7 +2,8 @@
 id: node
 title: Node.js
 ---
-## npm
+## Installation
+### npm
 Install with `npm`:
 
 ```bash
@@ -11,7 +12,7 @@ npm install katex
 npm install -g katex
 ```
 
-## Yarn
+### Yarn
 Install with `Yarn`:
 
 ```bash
@@ -20,8 +21,7 @@ yarn add katex
 yarn global add katex
 ```
 
-## Building from Source
-
+### Building from Source
 To build you will need Git, Node.js 6.9 or later, and Yarn.
 
 Clone a copy of the GitHub source repository:
@@ -36,5 +36,33 @@ yarn
 yarn build
 ```
 
+If you'd like to use the built KaTeX in other projects, install the package by
+specifying the path:
+```bash
+yarn add /path/to/KaTeX
+# or using npm
+npm install /path/to/KaTeX
+```
+
 > You can manually download the package and source code from
 [GitHub releases](https://github.com/Khan/KaTeX/releases).
+
+## Importing
+KaTeX is exported as a CommonJS module, which can be imported using `require`:
+```js
+const katex = require('katex');
+```
+
+If you're using a module loader, transpiler, or bundler that supports interoperability
+between ECMAScript module and CommonJS module, you can use `import`:
+```js
+import katex from 'katex';
+```
+
+KaTeX also provides an ECMAScript module:
+```js
+import katex from 'katex/dist/katex.mjs'
+```
+
+> The ES module contains ES6 syntaxes and features, and may need transpiling to
+use in old environments: