Make Info-mode respect INFOPATH

[abcdw]

Probably outside of envrc scope, but maybe you know a clean solution. How to make Emacs' info command to be aware of info pages provided via INFOPATH by project's .envrc?

[zackw]

I suspect this is another use case for envrc-post-update-hook, see #55 and #56.

[abcdw]

@hpfr, @purcell <3