feat: Add deploy instructions for QuantCDN.

[steveworley]

Summary

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• [ x] Docs
• Build-related changes
• Other, please describe:

If changing the UI of default theme, please provide the before/after screenshot:

Does this PR introduce a breaking change? (check one)

• Yes
• [ x] No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)

You have tested in the following browsers: (Providing a detailed version will be better.)

• Chrome
• Firefox
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• Edge
• IE

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature
• Related documents have been updated
• Related tests have been updated

To avoid wasting your time, it's best to open a feature request issue first and wait for approval before working on it.

Other information:

Hi there! I've been working on a static site hosting service with a bit of a twist, we provide an interface and version control to static pages with immediate publishing/unpublishing workflow support to blend static sites with traditional dynamic content management systems.

We want to support open-source by providing the service for free to open-source projects.

Hoping that we can including some information to support a different deployment target for the static output of vuepress! I've set up a boilerplate example to show off using vuepress+quantcdn!

• https://github.com/quantcdn/quant-vuepress-example
• ab819485-1f89-478e-a63f-a752a63f3eee-vuepress-example.quantcdn.io