Add notes about 3.0 update to README

README.md

@@ -10,3 +10,10 @@ Note that ido-ubiquitous is not enabled for org mode or magit mode,
 because those modes have their own built-in support for ido, which you
 should enable instead. Also, to enable ido for all file and buffer
 completion, customize `ido-everywhere`.
+
+ido-ubiquitous version 3.0 is a major update, including a split into
+two packages, and some of the configuration options have changed in
+non-backwards-compatible ways. If you have customized ido-ubiquitous,
+be sure to check out `M-x customize-group ido-ubiquitous` and `M-x
+customize-group ido-completing-read+` after updating to 3.0 and make
+sure the new settings are to your liking.

ido-ubiquitous.el

@@ -43,6 +43,14 @@
 ;; ido-ubiquitous' and read about the override variables for more
 ;; information.
 
+;; ido-ubiquitous version 3.0 is a major update, including a split
+;; into two packages, and some of the configuration options have
+;; changed in non-backwards-compatible ways. If you have customized
+;; ido-ubiquitous, be sure to check out `M-x customize-group
+;; ido-ubiquitous' and `M-x customize-group ido-completing-read+'
+;; after updating to 3.0 and make sure the new settings are to your
+;; liking.
+
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;;
 ;; This program is free software: you can redistribute it and/or modify