BUG Broken "How to Run Things Locally" link.

[pflagerd]

Describe the bug
As of this commit, on this page, there is a link How to Run Things Locally which points to a page which no longer exists on the threejs.org site.

To Reproduce
Steps to reproduce the behavior:

1. From a browser, navigate to https://discoverthreejs.com/book/introduction/about-the-book/
2. Search for the text "How to Run Things Locally"
3. The text is a hyperlink to https://threejs.org/docs/#manual/introduction/How-to-run-things-locally
4. Attempt to navigate to that URI.
5. Observe that the page is empty:

Expected behavior
Navigating to the link should result in seeing a page describing how to set up to run a threejs example on your local computer.