Portenta X8: FoundriesFactory: Improve Sources definition

Sync Sources description with Foundries.io documentation in
https://docs.foundries.io/latest/reference-manual/factory/factory-sources.html

Include detailed information on how to trigger builds and create
new targets.

Signed-off-by: Vanessa Maegima <vanessa.maegima@foundries.io>

Author: vanmaegima

content/hardware/04.pro/boards/portenta-x8/tutorials/x8-fundamentals/portenta-x8-fundamentals.md

@@ -51,12 +51,12 @@ Your Factory page allows you to add members, so that you can easily keep track o
 
 On the "source" page of your Factory, you can find the four repositories that are used to customize the images. These are:
 
-- **ci-scripts.git**: CI scripts to build images for all the machines that need to be built.
-- **lmp-manifest.git**: Index of the repositories to be downloaded by repository to create the source work tree.
-- **meta-subscriber-overrides.git**: Yocto layer containing Arduino specific customizations (machine definition, device drivers, etc). 
-- **containers.git**: Container recipes
+- **ci-scripts.git**: Scripts that define the platform and container build jobs to the FoundriesFactory continuous integration system.
+- **lmp-manifest.git**: The repo manifest for the platform build. It defines which layer versions are included in the platform image. This includes **meta-partner-arduino**, the layer containing Arduino specific customizations (machine definition, device drivers, etc).
+- **meta-subscriber-overrides.git**: OE layer that defines what is included into your factory image. You can add board specific customizations and overrides, add and remove packages provided in the default Linux microPlatform base.
+- **containers.git**: This is where containers and docker-compose apps are defined. It allows you to define what containers to build, and how to orchestrate them on the platform.
 
-While the "targets" page contains the images built by the Continuous integration system each time something is committed in the repositories. Committing to a repository will trigger building a target which can then be inspected in the "targets" page. Each target will compile for multiple platforms (as specified in the ci-scripts.git) and will generate all the required files to program the target.
+While the "targets" page contains the images built by the Continuous integration system each time something is committed in the repositories. Committing to **lmp-manifest.git** or **meta-subscriber-overrides.git** repositories will create a platform target, while committing to **containers.git** will create a container target. These targets will generate the artifacts for the platforms as specified in the **ci-scripts.git**, including all the required files to program the target in case of platform builds. You can inspect your FoundriesFactory targets in the "targets" page.
 
 ## Containers