Update INSTALL.md

Updated aptitude to apt-get install mysql-server mysql-client snmpd.
Dropped sudo - assumption user is authorized.
Merge pull request #10 from pandom/patch-1

Update INSTALL.md
Add root disclaimer, replace `aptitude` with `apt-get`
create new method for populating database
Merge branch 'master' of github.com:librenms/librenms
update instructions to use new database builder. clarify instructions.
remove redundant `on the nms` line and general formatting improvements
update INSTALL.md with minor corrections and updates

correct location of Apache config
add SSH method of git cloning the repo
add disclaimer that port needs to be open for chosen git cloning method.
add CentOS/RHEL install instructions
prevent 'ET phone home'

for now, simply commenting out the $dataHandle variable will prevent LibreNMS from sending stats.
Remove remaining live references to observium.org
Merge branch 'master' into devel