Change links script, add gitignore & secret files

Added secret files like .ssh to project but also listed them
in .gitignore since this repo is public on github.

Change create-home-links.sh to specify which files are linked in
home. This had to be done to allow .gem/credentials to be linked;
I don't want the entire .gem directory stored in here. Besides,
it makes the script more simple.

Also update README, make .npmrc secret since it includes _auth
and add .zshrc which simply sources ~/.bashrc.