Update quickstart.md

There is no Security Group, Network, or Subnet in this blueprint. There is only one VM.
Update quickstart.md

I added two short introductory notes to deployments and blueprints.
I also corrected the number of nodes described in the singlehost blueprint, fixed a few misspelled words, and fixed one or two typos.
Merge branch 'master' into review-guide-quickstart

Conflicts:
	guide/3.1/quickstart.md
Merge pull request #161 from cloudify-cosmo/review-guide-quickstart

Review guide quickstart