Unable to run - is what in your PATH?

On trying to use this, I get the below message. I did indeed run atom from the command line with 'atom .' but have no idea what "Is it in your PATH?" means. Can you advise what I should do to put 'it' in my path please? Ruby? Atom? and how would I do that? Google was not my friend on this. I don't find this message helpful. I'm using Linux Mint.

Thanks.
Tim.

Unable to run
ruby

Did you start Atom from the command line?
atom .

Is it in your PATH?
PATH: /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games

Start by reproducing the failure in Atom after launching it with `atom .`, using the PATH shown in the report. Determine whether the inability to run Ruby is caused by the reported environment or by atom-script, then document or verify the expected behavior and confirm the error message gives actionable guidance.

Written by the indexing model from the issue text.