infra: add MFM form for new post submission

[teauxfu]

• title (~50 characters)
• description/abstract: 2-3 sentences
• optional header image below title. keep phone resolution in mind. prefer short, wide photos. see DSA resources graphics folder
• author(s) to list? name or chapter?
• link to article text (MFM/Drive/attachment)
• when do you want it to be published? (at least one week out for editorial review)