Suggest using appstream-util from flatpaked flatpak-builder

That is used on Flathub and in the linter right now instead of the
appstream-glib flatpak

docs/02-for-app-authors/02-requirements.md

@@ -201,7 +201,7 @@ Do note that CLI applications do not require a `.desktop` file but TUI applicati
 
 ### Appstream
 
-Appstream is the standard used to provide metadata about applications. Applications must provide appstream data and pass `flatpak run org.freedesktop.appstream-glib validate`. If application metadata has not been provided by the upstream, it should be licensed with [Creative Commons Zero, version 1](https://creativecommons.org/choose/zero/), by stating `CC0-1.0` in `metadata_license`.
+Appstream is the standard used to provide metadata about applications. Applications must provide appstream data and pass [validation](/docs/for-app-authors/appdata-guidelines/#use-flathubs-appstream-util). If application metadata has not been provided by the upstream, it should be licensed with [Creative Commons Zero, version 1](https://creativecommons.org/choose/zero/), by stating `CC0-1.0` in `metadata_license`.
 
 In [AppData guidelines](appdata-guidelines) you'll find tips/best practices to help you get your AppData up to spec. For information about appstream, see [its documentation](https://www.freedesktop.org/software/appstream/docs/index.html).
 

docs/02-for-app-authors/03-appdata-guidelines/index.md

@@ -11,9 +11,8 @@ These guidelines are curated for Flathub use-cases, they don’t cover anything
 Flathub uses modified `appstream-util` to validate AppData during build. To run the same check locally, you can install and run it with a simple:
 
 ```bash
-flatpak install flathub org.freedesktop.appstream-glib
-flatpak run org.freedesktop.appstream-glib validate tld.domain.appid.metainfo.xml
-tld.domain.appid.metainfo.xml: OK
+flatpak install -y flathub org.flatpak.Builder
+flatpak run --command=appstream-util org.flatpak.Builder validate tld.domain.appid.metainfo.xml
 ```
 
 ## Path and filename