New review comment by mhmdanas on void-packages repository

https://github.com/void-linux/void-packages/pull/44649#discussion_r1242686916

Comment:
```suggestion
As a special case, `virtual` dependencies may be specified as runtime dependencies in the
`depends` template variable. Several different packages can provide common functionality by
declaring a virtual name and version in the `provides` template variable (e.g.
`provides="vpkg-0.1_1"`). Packages that rely on the common functionality without concern for the
specific provider can declare a dependency on the virtual package name with the prefix `virtual?`
(e.g., `depends="virtual?vpkg-0.1_1"`). When a package is built by `xbps-src`, providers for any
virtual packages will be confirmed to exist and will be built if necessary. A map from virtual
packages to their default providers is defined in `etc/defaults.virtual`. Individual mappings can be
overridden by local preferences in `etc/virtual`. Comments in `etc/defaults.virtual` provide more
information on this map.
```