Improve account_invoice_stock documentation

Documentation improvements as part of the GSoD: https://discuss.tryton.org/t/gsod-project-documentation-for-basic-modules/3186

assigned to @dave

added accounting type::feature + 1 deleted label

added 1 deleted label and removed 1 deleted label

It is missing the review.

So it is, I'm not sure why? I uploaded the review in the same way as the other ones.

review316221002 updated at https://codereview.tryton.org/316221002/#ps324461002

review316221002 updated at https://codereview.tryton.org/316221002/#ps304881002

review316221002 updated at https://codereview.tryton.org/316221002/#ps329751002

review316221002 updated at https://codereview.tryton.org/316221002/#ps319031002

New changeset 8a5e54db6bda by David Harper in branch 'default':
Improve documentation
https://hg.tryton.org/modules/account_invoice_stock/rev/8a5e54db6bda

added 1 deleted label and removed 1 deleted label

closed

New changeset cdf4f72dab94 by David Harper in branch 'default':
Improve documentation
https://hg.tryton.org/tryton-env/rev/cdf4f72dab94