Clarify doom-store-put docstring
Clarify doom-store-put docstring

Explicitely states that a `nil` TTL means "no expiration"

Make it clearer that TTL is an offset to current-time, and not a timestamp in seconds
hlissner/.emacs.d,hlissner/doom-emacs,hlissner/.emacs.d,hlissner/.emacs.d,hlissner/.emacs.d,hlissner/doom-emacs,hlissner/doom-emacs,hlissner/doom-emacs,hlissner/doom-emacs,hlissner/doom-emacs,hlissner/.emacs.d,hlissner/doom-emacs,hlissner/.emacs.d,hlissner/.emacs.d,hlissner/.emacs.d