.adr-dir as the root of a tree

[NielsDoucet]

Providing a different perspective on the feature request in #51

We're looking into using this tool to manage a centralised adr repository for adrs spanning multiple repos and teams.
For organisational purposes we would like to reflect our internal team structure through the usage of (sub-)directories.
Would it be possible to have the adr new command accept a relative path to the root (where adr init was run/where .adr-dir points to).
I do recognise this would probably create problematic interactions with the link and supersede functionality but I'm open for a discussion on those potentially problematic areas.