Create markdown file for forms guidance

[bonnieAcameron]

In order for @jaclinec to make the updates to her forms guidance, she needed help converting the guidance into markdown.

[bonnieAcameron]

Usability Guidance for Required Fields

Do:

• Show whether a field is required or optional. Mark required fields as required by using a red asterisk *
• Combine the red asterisk * with a text description at the top of the form instructing the user of its meaning.

Example: “A red asterisk * indicates a required field.”

• Add the required attribute to any specific form elements that are required to let users of assistive technologies know this is a required field.
• Label optional fields with the word “optional” placed in parentheses.

Example: (optional)

• Error handling: Use a message or alert to notify the user if a field that is required was not completed, and indicate which field was not completed. Additionally, include an error notification in the page title (title element) for screen readers.

Note: One-field forms are the exception and do not need to be marked with a required label or symbol.

[bonnieAcameron]

This is done @brunerae and @thisisdano and the work is continued in #1834