RFC 003 does not list source tool

[Dan33l]

In the RFC 0003, no source tool is listed as accepted with pdk release command.

With PDK PR PR 809 a first step is provided with Github as source. But the RFC was not Github specific. It looks useful to talk about sources planed.

[scotje]

I think that requirement is coming from Github Changelog Generator which will be made an optional part of pdk release process in a future revision.