Update README.md

Author: RobThree

README.md

@@ -183,9 +183,11 @@ The generated 2.x ID's are still compatible with 3.x ID's. This release is mostl
 
 # FAQ
 
-**Q**: Help, I'm getting duplicate ID's?
+**Q**: Help, I'm getting duplicate ID's or collisions?
 
-**A**: Then you're probably not using IdGen as intended: It should be a singleton, and if you insist on having multiple instances around they should all have their own unique GeneratorId
+**A**: Then you're probably not using IdGen as intended: It should be a singleton (per thread/process/host/...), and if you insist on having multiple instances around they should all have their own unique GeneratorId.
+
+**A**: Also: Don't change the structure; once you've picked an `IdStructure` and go into production commit to it, stick with it. This means that careful planning is needed to ensure enough ID's can be generated by enough generators for long enough. Although changing the structure at a later stage isn't impossible careful consideration is needed to ensure no collisions will occur.
 
 **Q**: I'm experiencing weird results when these ID's are used in Javascript?