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.
Update index.html
Merge pull request #169 from kannes/patch-1

Update index.html
update avatar
Nächstes Event Chemnitz
changes index.html for berlin
Update events.yml
Update events.yml
Update events.yml
new date in cologne
Merge pull request #171 from marcel12bell/gh-pages

new date for cologne
added mailing list address
Merge pull request #172 from codeforHH/gh-pages

added mailing list address
Update events.yml
Update index.html
giessen: changed eventdate, added twitter, added new member
Merge pull request #173 from serofax/gh-pages

giessen: changed eventdate, added twitter, added new member
Update index.html
Merge pull request #174 from balzer82/patch-1

Update index.html
update avatars