fix pkg level documentation

[rCarto]

You have file 'osrm/man/osrm.Rd' with \docType{package}, likely intended as a package overview help file, but without the appropriate PKGNAME-package \alias as per "Documenting packages" in R-exts.

This seems to be the consequence of the breaking change

Using @docType package no longer automatically adds a -package alias. Instead document _PACKAGE to get all the defaults for package documentation.

in roxygen2 7.0.0 (2019-11-12) having gone unnoticed, see https://github.com/r-lib/roxygen2/issues/1491.

As explained in the issue, to get the desired PKGNAME-package \alias back, you should either change to the new approach and document the new special sentinel

"_PACKAGE"