Tell people not to be the BOFH.

This is a start to the "how not to be a sysadmin" section. I've tried to
achieve some balance between useful guidance and preaching.
content for airco, security in datacenters

Filled some content for review
Added screen usage
adding initial content to hardware
Point people at github's git docs for now

We'll want to actually cover git and github in the curriculum, for sure.
For now, pointing people to the docs Github have already written should
provide at least some useful info. I've also pointed people at the IRC
channel if github's docs are insufficient.
Fix the tyop, thanks Mike
Merge pull request #91 from apeiron/topic/apeiron/git-github-docs

Point people at github's git docs for now
updates links for some redirects and remote vs local
whitespace removals
Merge branch 'master' of https://github.com/FlorianHeigl/curriculum into FlorianHeigl-master
Fixing warnings for list indentation
whitespace removals
datacenters 201: typos
Merge branch 'master' into topic/apeiron/what-sysadmin-is-not

Conflicts:
	sysadmin_101.rst
Merge pull request #93 from apeiron/topic/apeiron/what-sysadmin-is-not

Elaborate a bit on what sysadmin is not
IssueID #89 - TODO List - firewalls on host vs network
https://github.com/opsschool/curriculum/issues/89
Talk about running firewalls on host vs network
Modified:
security_201.rst
IssueID #89 - TODO List - firewalls on host vs network
https://github.com/opsschool/curriculum/issues/89
Added real world example
Modified:
security_201.rst
Fix merge conflicts in sysadmin_tools.rst
IssueID #89 - TODO List - firewalls on host vs network
https://github.com/opsschool/curriculum/issues/89
Talk about running firewalls on host vs network - rebase and some modifications
Modified:
security_201.rst
Adressing pull request concerns.