pt-online-schema-change plugin documentation is incomplete

[Nilnandan Joshi]

From the pt-online-schema-change documentation: https://www.percona.com/doc/percona-toolkit/2.2/pt-online-schema-change.html

"--plugin
type: string

Perl module file that defines a pt_online_schema_change_plugin class. A plugin allows you to write a Perl module that can hook into many parts of pt-online-schema-change. This requires a good knowledge of Perl and Percona Toolkit conventions, which are beyond this scope of this documentation. Please contact Percona if you have questions or need help.

See "PLUGIN" for more information."

This is incredibly unhelpful, and there are very few examples of working plugins other than Sam Lambert's:
https://github.com/samlambert/pt-online-schema-change-analyze/blob/master/pt-online-schema-change-analyze.pl

Please consider adding an empty or example pt_online_schema_change package to your documentation.

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PT-696