Replace my.cdn in code sample with example.com

[d34dman]

The code samples in Usage with CDN is not clear enough. One might copy paste it and expect to work. Which would not, since the links are placeholders and needs to be replaced with actual entries from CDN.

This PR aims to make it little more obvious that, they are example links.

I used example.com because,

• It is a reserved domain for such cases, more info in this wiki page.
• It would provide a nice feedback to the user while reading the code it self.
• Visiting the urls won't result in an error, and give a page stating that it is used for example purpose.

As a bonus, am wondering if this also future proofs it, in case somebody do register my.cdn and use the link for malicious purpose.

[github-actions]

No JS Changes

Generated by 🚫 dangerJS against e989dde

[mAAdhaTTah]

The other idea I had when I was doing this last night is to use Handlebars syntax {{cdn}} or something like that so it's very clearly a placeholder/variable.

[RunDevelopment]

So something like https://{{cdn}}/prism@v1.x/themes/prism.css?

Sounds good. It's short and unambiguous.

[d34dman]

@RunDevelopment I have done the changes requested, please review :)

[RunDevelopment]

Thank you for contributing @d34dman!