Add organiser handbooks

[mvdan]

We could start with:

Treasury:

• Finding new sponsors
• Current sponsorship tiers and amounts
• Invoicing and renewing sponsors
• Keeping track of the finances
• Using the bank account and debit cards

Social Media:

• Writing style and general tips
• Tweeting about upcoming events
• Tweeting during events
• @-mentioning speakers and sponsors

Speakers:

• Rules for talks; 15 minutes, etc
• Use of a form to receive applications
• Encouraging new and recurrent speakers
• Mentoring speakers who need it

Event running:

• Handling of our only venue so far
• Planning and announcing future events
• Preparing the MC slides
• General tips on opening and closing each meetup