[Borgbackup] borg internals narrative

[Antoine Beaupré]

This diagram was copied to:

https://github.com/jborg/attic/issues/216

this wasn't dealt with in borg yet either:

https://github.com/jborg/attic/pull/223

... but probably should.

a.
-- 
O gentilshommes, la vie est courte.
Si nous vivons, nous vivons 
pour marcher sur la tête des rois.
                        - William Shakespeare