Update README.md with Do not reference sys_choice table desc

Author: niamccash

README.md

@@ -229,6 +229,9 @@ Restrict the number of row counts ma x to 10,20,50 instead of higher limits such
 Navigate to the user preference <sys_user_preference> table and search by 'rowcount'. Set the value to 50 max.
 Also, can set the property 'glide.ui.per_page' sys property value to 10, 20, 50 only
 
+### Do not reference sys_choice table
+The Choice table should not be used as the reference table for a Reference type field. Reference fields store the sys_id of the corresponding record in the reference table and show the specified display value. For example: the caller_id field stores the sys_id of a record from the user table and displays the corresponding name value. This presents a problem when using the sys_choice table, because existing records are deleted and replaced when choices are modified. This causes a new sys_id to be generated for each record in the choice list. So the sys_id stored in the Reference field is no longer a valid value and the reference is broken.
+
 
 ## Category: Security
 ##Check Mandatory fields on incident