PACKAGING.md: add new virtual package requirement

Author: majewsky

CHANGELOG.md

@@ -31,6 +31,8 @@ Packagers beware:
 
 - Because of the switch to Go modules, the build system now expects Go 1.14 or newer. Older Go versions might still
   work, but you may have to patch or substitute the build invocation in the `build/holo` make target.
+- Packages should add a `Provides` relation on the virtual package `holo-generators` since holo-build will generate
+  dependencies on that package when files are installed to `/usr/share/holo/generators`.
 
 Bugfixes:
 

PACKAGING.md

@@ -26,4 +26,4 @@ Holo includes several plugins for itself. Since
 [holo-build](https://github.com/holocm/holo-build) will also generate
 dependencies on these, the `holo` package must have a Provides relation (or
 whatever this is called in your package format) to `holo-files`,
-`holo-run-scripts`, `holo-ssh-keys` and `holo-users-groups`.
+`holo-generators`, `holo-run-scripts`, `holo-ssh-keys` and `holo-users-groups`.