update apt cache

Depending on the image state we could need to update apt cache otherwise the first "apt-get install" fails
Merge pull request #7 from cscetbon/patch-1

update apt cache
Add example session to GitHub README
Improve session gif in GitHub README
fix issue 8: dnsmasq: setting capabilities failed: Operation not permitted, by adding user=root entry to dnsmasq.conf
Merge pull request #9 from tsindot/master

fix issue 8: dnsmasq: setting capabilities failed: Operation not permitted
Add a demo Vagrantfile for vagrant users