docs: update documentation for res.type() (#1783)

Signed-off-by: Dustin Popp <dustinpopp@ibm.com>

_includes/api/en/4x/res-type.md

@@ -14,3 +14,5 @@ res.type('application/json')
 res.type('png')
 // => 'image/png'
 ```
+
+Aliased as `res.contentType(type)`.

_includes/api/en/5x/res-type.md

@@ -1,6 +1,6 @@
 <h3 id='res.type'>res.type(type)</h3>
 
-Sets the `Content-Type` HTTP header to the MIME type as determined by the specified `type`. If `type` contains the "/" character, then it sets the `Content-Type` to the exact value of `type`, otherwise it is assumed to be a file extension and the MIME type is looked up in a mapping using the `express.static.mime.lookup()` method.
+Sets the `Content-Type` HTTP header to the MIME type as determined by the specified `type`. If `type` contains the "/" character, then it sets the `Content-Type` to the exact value of `type`, otherwise it is assumed to be a file extension and the MIME type is looked up using the `contentType()` method of the `mime-types` package.
 
 ```js
 res.type('.html') // => 'text/html'
@@ -9,3 +9,5 @@ res.type('json') // => 'application/json'
 res.type('application/json') // => 'application/json'
 res.type('png') // => image/png:
 ```
+
+Aliased as `res.contentType(type)`.

en/guide/migrating-5.md

@@ -37,6 +37,7 @@ You can then run your automated tests to see what fails, and fix problems accord
   <li><a href="#res.send.body">res.send(body, status)</a></li>
   <li><a href="#res.send.status">res.send(status)</a></li>
   <li><a href="#res.sendfile">res.sendfile()</a></li>
+  <li><a href="#express.static.mime">express.static.mime</a></li>
 </ul>
 
 **Changed**
@@ -262,6 +263,20 @@ app.get('/user', (req, res) => {
 })
 ```
 
+<h4 id="express.static.mime">express.static.mime</h4>
+
+In Express 5, `mime` is no longer an exported property of the `static` field.
+Use the [`mime-types` package](https://github.com/jshttp/mime-types) to work with MIME type values.
+
+```js
+// v4
+express.static.mime.lookup('json')
+
+// v5
+const mime = require('mime-types')
+mime.lookup('json')
+```
+
 <h3>Changed</h3>
 
 <h4 id="path-syntax">Path route matching syntax</h4>