[META] Guidelines to add to the docs

[snide]

As part of our internal EUI satisfaction survey we got a pretty consistent request to add more guidelines to EUI. Here are some topics of common patterns where we see irregularity when a designer is not directly involved in the project.

If you run into confusion in EUI, please leave a comment and add a suggestion and we'll adjust the list. This will become more of a priority with our team as the library continues to mature.

• Empty states ([Spec] Empty states pattern #3564)
• Permission blockers (Align wrong/missing permissions messages on Management UI kibana#35796)
• Login screens
• Form layouts and validation (include general understanding of how label/id's work with EuiFormRow)
• When fixed layouts are helpful
• When to disable vs. hide button actions
• Table layouts
• "Panel" forms like Canvas and Maps
• Multi-step wizards
• General page layout and title hierarchy
• Super Date Picker (needs to be it's own page)
• Anchor vs Button tags and when to use onClick vs href
• Tours

[ryankeairns]

A recent Slack chat led us to summarize form validation as follow:

• Focus on first item
• Validate format/syntax onBlur (preferred over onChange so as to avoid validation errors as you start typing your initial input)
• Validate required fields onSubmit
• Don’t disable the button (screen readers may bypass it; if you can't click, you can't see what's remaining)

[cchaos]

I've added each of these bullet points to the Guidelines column of the Documentation project. I find this organization easier to track.