OSDOCS-11188: adds note about greenboot.conf customization persistence MicroShift

Author: ShaunaDiaz

modules/microshift-greenboot-dir-structure.adoc

@@ -39,3 +39,11 @@ Returning a nonzero exit code from any script means that script has failed. Gree
 * `/etc/greenboot/green.d` contains scripts that run after Greenboot has declared the start successful.
 
 * `/etc/greenboot/red.d` contains scripts that run after Greenboot has declared the startup as failed, including the `40_microshift_pre_rollback.sh` prerollback script. This script is executed right before a system rollback. The script performs {microshift-short} pod and OVN-Kubernetes cleanup to avoid potential conflicts after the system is rolled back to a previous version.
+
+[IMPORTANT]
+====
+If you customize the values of any environment variable in the `/etc/greenboot/greenboot.conf` file, these changes can be lost when the greenboot RPM package is updated or downgraded.
+
+* To retain customizations when building system images with {microshift-short}, add the `greenboot.conf` file to a blueprint.
+* To retain customizations when using an RPM installation, apply changes to the `greenboot.conf` file after you install {microshift-short} and greenboot RPMs.
+====