Make it clear that Chocolatey CLI requires administrator privileges when it is run for the first time

Based on [this comment](https://github.com/chocolatey/choco/issues/1048#issuecomment-285680722) we should look to make it clear that the Chocolatey CLI requires administrator privileges to run the first time and that by running it without those privileges the users experience will be limited. Managing software installations on Windows requires administrator privileges that are dictated by the Operating System.

Start by locating the Chocolatey CLI installation or first-run documentation in the docs site and review the linked discussion for the intended wording. Done means the documentation clearly explains the administrator-privilege requirement on first use and the limitations of running without it.

Written by the indexing model from the issue text.