Clarify the meaning of remote when giving NGen image run options

[jameshalgren]

TL;DR

This fixes confusing language in the guide script. Please feel free to suggest something better.

More detail

The guide script has a prompt to give the user the option to run with an existing container or to pull a 'fresh' version from the docker repository.

This commit changes the language in that prompt from a somewhat confusing:

1) Run NextGen Model using local docker image
2) Run Nextgen using remote docker image
3) Exit

(aren't all docker images local? what am I getting in a remote image?)

... to the (hopefully) more clear:

1) Run NextGen using existing local docker image	      
2) Run NextGen after updating to latest docker image
3) Exit

The idea is that the #1 "local" run does not go recompile or rebuild anything, so it might be the best option if you have a setup that is working and you simply want to re-run to reproduce a result (or see a new result from a slightly modified ngen realization, etc.) The #2 "remote" option goes to dockerhub and grabs the latest updates -- useful if you are having problems or trying to test out recently released functionality.

(Note -- changed "NextGen Model" to just "NextGen" to reflect the standard language.)

[jameshalgren]

This is a one-liner.Do the lines in the select-case statement immediately following also need to be updated?
Answer -- yes they do. Converting to draft until fixed...
Fixed. Ready for review.