use GH url for remote

[topepo]

The remotes or pak packages can't install the GH version of mirai since the remote for doesn't include the repo name:

> pak::pak("shikokuchuo/mirai", ask = FALSE)
✔ Loading metadata database ... done                          
Error:                                                                     
! error in pak subprocess
Caused by error: 
! Could not solve package dependencies:
* shikokuchuo/mirai: Can't install dependency nanonext (>= 1.2.1.9002) 

This PR adds that to remotes:.

[shikokuchuo]

Thanks! Ive added a remotes field instead otherwise it won't install locally. pak should then pick it up.

[shikokuchuo]

Or else set repos to shikokuchuo.r-universe.dev. R-universe is really convenient in this respect.

FYI the intention has always been to stagger releases so dev mirai would only depend on release nanonext, but alas the development is so tightly integrated, this has rarely been possible!