better alternative to environment variables?

[AlexaVillaume]

          I don't think adding an environment variable is the right way to go. This will mean that users will have to add this as part of the install process which can be annoying. Using relative imports and paths should be able to handle most of these cases. If it is an issue keeping track of where the isochrones are stored, we may want to think about having the user specify where these are stored as an input to the isochrone object instead of trying to hide the lookup tables in the directory structure of the code

Originally posted by @ConnorStoneAstro in #35 (comment)