docs(default-flatpaks): Add known issue about #231 (#232)

modules/default-flatpaks/README.md

@@ -35,3 +35,9 @@ https://github.com/blue-build/modules/issues/146
 
 Flatpak runtimes are not supported due to technical difficulty in implementing those:  
 https://github.com/blue-build/modules/pull/142#issuecomment-1962458757
+
+Flatpak IDs input in the last module definition overwrites the 1st one.  
+This scenario happens when multiple module definitions of `default-flatpaks` are used.  
+This means that the only flatpak list that is going to take the effect is the one in last module definition.  
+More details about this issue:
+https://github.com/blue-build/modules/issues/231