[TODO] Support reno by checking its config at config.yaml

[webknjaz]

This is a follow-up for #1.
We need to allow users to set an option in the Chronographer App corresponding --rel-notes-dir|-d CLI arg of reno.
We need to use notesdir from config.yaml option to identify the target subdirectory for changelog fragments.
Combining those two options will give us a full path to the fragments dir.
Finally, config.yaml contains a sections list which contains pairs of values of file extension type and its title.