fix link in documentation_style_guide.md

[lottihill]

Resolves #7050

Changes:

Added the missing link in the sentence:
'Use the idioms recommended in this guide.'

Now links to:
https://github.com/processing/p5.js/blob/main/contributor_docs/contributing_to_the_p5.js_reference.md

Screenshots of the change:

Before

After

[welcome]

🎉 Thanks for opening this pull request! Please check out our contributing guidelines if you haven't already. And be sure to add yourself to the list of contributors on the readme page!

[limzykenneth]

@lottihill Sorry I think I misunderstood what you were asking before. The "this guide" mentioned in the changes you made here refers to the current document instead of the document being linked to in this PR. The link that needs to be changed is this one.

For the "this guide" I think it can potentially be linked somewhere in this document, @nickmcintyre can probably provide a bit more context.

[Qianqianye]

Thanks @lottihill. Closing this PR because it's fixed in #7053