Update preview mode example to say draft mode (vercel#699)

### Description

We're changing the name of Preview Mode to Draft mode.
- [Next docs
update](https://nextjs.org/docs/pages/building-your-application/configuring/draft-mode)

Vercel docs updates are in the works.

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### Demo URL

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### Type of Change

- [ ] New Example
- [x] Example updates (Bug fixes, new features, etc.)
- [ ] Other (changes to the codebase, but not to examples)

### New Example Checklist

- [ ] 🛫 `npm run new-example` was used to create the example
- [ ] 📚 The template wasn't used but I carefuly read the [Adding a new
example](https://github.com/vercel/examples#adding-a-new-example) steps
and implemented them in the example
- [ ] 📱 Is it responsive? Are mobile and tablets considered?

---------

Co-authored-by: Steven <[email protected]>

build-output-api/preview-mode/.vercel/output/functions/index.func/index.js → build-output-api/draft-mode/.vercel/output/functions/index.func/index.js

@@ -4,17 +4,17 @@ const bypassToken = '87734ad8259d67c3c11747d3e4e112d0'
 
 module.exports = (req, res) => {
   res.setHeader('Content-Type', 'text/html; charset=utf-8')
-  const isPreviewMode =
+  const isDraftMode =
     typeof req.headers.cookie === 'string' &&
     req.headers.cookie.includes(`__prerender_bypass=${bypassToken}`)
-  const contents = isPreviewMode
-    ? 'Preview Mode is <strong>ENABLED</strong>. Notice how the "Server time" below gets updated every time you refresh!'
-    : 'Preview Mode is <strong>DISABLED</strong>. The "server time" below will only get updated once per minute.'
-  const enable = isPreviewMode
-    ? '<a href="/logout">Deactivate Preview Mode</a>'
-    : '<a href="/login">Enable Preview Mode</a>'
+  const contents = isDraftMode
+    ? 'Draft Mode is <strong>ENABLED</strong>. Notice how the "Server time" below gets updated every time you refresh!'
+    : 'Draft Mode is <strong>DISABLED</strong>. The "server time" below will only get updated once per minute.'
+  const enable = isDraftMode
+    ? '<a href="/logout">Deactivate Draft Mode</a>'
+    : '<a href="/login">Enable Draft Mode</a>'
   res.end(`
-<h1>Preview Mode Example</h1>
+<h1>Draft Mode Example</h1>
 <p>${contents}</p>
 <p>Server time: ${new Date().toISOString()}</p>
 <p>${enable}</p>

build-output-api/draft-mode/README.md

@@ -0,0 +1,18 @@
+# Draft Mode
+
+## Build Output API
+
+This Prebuilt Deployment example demonstrates how to implement "Draft Mode" when using the [Build Output API](https://vercel.com/docs/build-output-api/v3#features/draft-mode).
+
+### Demo
+
+https://build-output-api-draft-mode.vercel.sh
+
+### How it Works
+
+When using Prerender Functions, you may want to implement "Draft Mode" which would allow you to bypass the caching
+aspect of prerender functions, i.e. while writing draft blog posts before they are ready to be published.
+
+To implement this, the `bypassToken` of the [`<name>.prerender-config.json`](./.vercel/output/functions/index.prerender-config.json) file should be set to a randomized string that you generate at build-time. This string should not be exposed to users / the client-side, except under authenticated circumstances.
+
+To enable "Draft Mode", a cookie with the name `__prerender_bypass` needs to be set (i.e. by a Serverless Function) with the value of the `bypassToken`. When the Prerender Function endpoint is accessed while the cookie is set, then "Draft Mode" will be activated, bypassing any caching that Vercel would normally provide when not in Draft Mode.