The Changes and README files are two free-form files, though the the Changes files usually have a common form. Recently work has been done to create a specification for the Changes file.

Even the name of the Changes file is not standardizd. Some people write CHANGES, others write Changes, yet others write ChangeLog.

It usualy includes entries for each release with the version number and date of release, and then a list of major changes. Sometime indicating the bug number that were fixed or the person who sent in those changes. 

v0.02 2007.11.23

    Added feature for doing something
    Fixed strange bug causing trouble (#7)


v0.01 2007.10.12

    Releasing first version of Application

The README file used to be important before CPAN had a web interface, today it is quite unclear what should be in it.

brian d foy had an article discussing this