Move content from Wiki to proper meetups files

[petros]

The history of our meetups is split. Some is in the wiki, and now we are using the meetups folder in the main repository itself. We want to move everything from the wiki to the folder in the main repository. And we also want to restructure the content in the meetups folder to match the practices we are following nowadays (i.e. one file per meetup, not a folder per meetup).