Add guideline about chaining to style guide

[meezwhite]

Increasing access

Improve style guide to prevent future inconsistencies in docs.

Most appropriate sub-area of p5.js?

• Contributor Docs (style guide)

Feature enhancement details

In reference to #6400 (comment), as proposed by @nickmcintyre, to add guideline about chaining functions to styleguide.

// Nope.
fill(0)
  .strokeWeight(0)
  .textSize(10);

// Nope.
fill(0).strokeWeight(0).textSize(10);

// Yep.
fill(0);
strokeWeight(0);
textSize(10);

[Anayverma]

Hey @meezwhite I would like to work on this issue. Please assign it to me.

[limzykenneth]

Yes I think that is fine to add, @meezwhite you can go ahead with a PR if you like.