Update presentation

[HerrBertling]

• Add slide about CSSClasses history
• Add slide about "Onboarding" at the end of the presentation
• Add slide about sponsoring of food/drinks
• Add slide about opportunity to present other meetups
• Add slide about what the coaches are doing and not doing today
• Add slide about photos/social media posts
• Add slide about location (smoking/restrooms/…)
• Add slide about what will happen today
• Add slide about what will not happen today
• Add slide to get all coaches to the front in order to "show" them to the participants