Validate the form for generating security.txt files

[joker314]

It'd be great to make sure people creative valid security.txt files. Some validation could include:

• Verifying that a : was included in the value of the Contact: directive (this would catch people who don't include mailto: and just put an email address directly) -- this error could probably be ignorable.
  This could also apply to [and even be a bit stricter there (require URLs only, for example)]
  • Policy
  • Hiring
• Ensuring that a Contact: directive is set
• Ensuring that the Preferred-Languages directive only contains commas, dashes, spaces, and letters