doc: document baloo re-indexing

- `services.keyd` changed API. Now you can create multiple configuration files.

- `baloo`, the file indexer/search engine used by KDE now has a patch to prevent files from constantly being reindexed when the device ids of the their underlying storage changes. This happens frequently when using btrfs or LVM. The patch has not yet been accepted upstream but it provides a significantly improved experience. When upgrading, reset baloo to get a clean index: `balooctl disable ; balooctl purge ; balooctl enable`.

- `services.ddclient` has been removed on the request of the upstream maintainer because it is unmaintained and has bugs. Please switch to a different software like `inadyn` or `knsupdate`.

- The `vlock` program from the `kbd` package has been moved into its own package output and should now be referenced explicitly as `kbd.vlock` or replaced with an alternative such as the standalone `vlock` package or `physlock`.