Updated installation instructions

Split the installation instructions into different sections. Added a section to
explain how to do installation just for the project using Bundler.

Also added instructions how to run jekyll if Bundler has been used to install
the gems.
Updated event for Leipzig
Merge pull request #176 from CodeforLeipzig/update-events

Updated event for Leipzig
Meetup OK Lab Ulm
heilbronn: august event
Update events.yml
Add Marc to berlin member list
Merge pull request #177 from dirkschumacher/patch-1

Add Marc to berlin member list
München: add mailinglist, twitter, and two more leads
Merge pull request #178 from jancborchardt/patch-1

München: add mailinglist, twitter, and two more leads
new date for cologne meetup
Merge pull request #179 from marcel12bell/gh-pages

new date for cologne meetup & new member
update description on ok labs
Change text
added new dates for giessen
added new badeseen project
Merge pull request #180 from serofax/gh-pages

Giessen: added new project and new events
added events until september
added kneipenplan
Merge pull request #181 from ironjan/paderborn

Paderborn