Add checklist and instructions updating and tophatting documentation changes

[dpersing]

WHY are these changes introduced?

Currently we don't consistently check to see if documentation needs to change when we make updates to a component.

WHAT is this pull request doing?

Adds PR checklist items for:

• Updating the component README.md (if necessary)
• Tophatting that documentation change in the style guide (if it is visible there)

[amrocha]

I think this might be confusing since there's multiple README.md files in the repo, can you use language that's bit more specific like if you modified a component, then update that component's README file or something like that

[dpersing]

Updated to specify the component-level README.md.

[amrocha]

This would be nice to include too but there's no easy way of doing this check right now. What if we told people to check in a MD previewer, do you think that's enough? We could also write a quick doc for how to tophat changes in the styleguide and link it here too

[dpersing]

We could also write a quick doc for how to tophat changes in the styleguide and link it here too

Can do. I think testing the look in the style guide is important, since folks in lots of different roles need to do it.

[amrocha]

Sounds good, it should just be a matter of documenting the build-consumer command and telling people to set up polaris-styleguide as well 👍

[dpersing]

Added a new doc, copying over some info from the Tophatting.md doc and adding instructions.

[amrocha]

Looks good to me, I'll let Selene review the content

[ry5n]

This is fantastic. Thanks @dpersing!

I did notice one typo in the new tophatting doc (see below).