Update README

Add some info about Chef Workstation and rbenv.

README.md

@@ -1,4 +1,15 @@
-### Install dependencies
+### Install Chef Workstation
+
+* macOS, Windows, RHEL, Ubuntu: https://docs.chef.io/workstation/install_workstation/
+* Arch Linux: https://aur.archlinux.org/packages/chef-workstation
+
+#### rbenv
+
+If you use rbenv to manage Ruby versions on your system, install the
+(rbenv-chef-workstation)[https://github.com/docwhat/rbenv-chef-workstation]
+plugin.
+
+### Install gem dependencies
 
     bundle install