Update docs

readme.md

@@ -25,6 +25,9 @@ No change is needed: it works exactly the same now as it did before!
 
 ## Install
 
+This package is [ESM only](https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c):
+Node 12+ is needed to use it and it must be `import`ed instead of `require`d.
+
 [npm][]:
 
 ```sh
@@ -36,15 +39,15 @@ npm install remark-vdom
 Say we have the following file, `example.js`:
 
 ```js
-var unified = require('unified')
-var markdown = require('remark-parse')
-var vdom = require('remark-vdom')
+import {unified} from 'unified'
+import remarkParse from 'remark-parse'
+import remarkVdom from 'remark-vdom'
 
 unified()
-  .use(markdown)
-  .use(vdom)
-  .process('Some _emphasis_, **importance**, and `code`.', function(err, file) {
-    if (err) throw err
+  .use(remarkParse)
+  .use(remarkVdom)
+  .process('Some _emphasis_, **importance**, and `code`.')
+  .then((file) => {
     console.dir(file.result, {depth: null})
   })
 ```
@@ -122,7 +125,10 @@ VirtualNode {
 
 ## API
 
-### `remark().use(vdom[, options])`
+This package exports no identifiers.
+The default export is `remarkVdom`.
+
+### `unified().use(remarkVdom[, options])`
 
 Compile Markdown to [Virtual DOM][vdom].