Problem: CONTRIBUTING.md does not reflect current workflow

Version of the documentation

v1.16

https://github.com/artefactual/archivematica/commit/1b93796d85464796d85e704c78e09cbee8c112d3

Page (and section, if applicable) where the issue occurs

CONTRIBUTING.md

https://github.com/artefactual/archivematica/blob/1b93796d85464796d85e704c78e09cbee8c112d3/CONTRIBUTING.md

Description of the issue

After having worked on Archivematica and its documentation for some months, I notice that the CONTRIBUTING.md has fallen out of touch with current practices. Here is a list of what I plan on updating. If I am missing something please comment.

Suggested fix

[x] In this reference to the Issues repo wiki - I notice that there no more wiki at the link, nor in that repo in general. Usually, we try to open issues and then link to PRs, and maybe we could suggest that workflow instead?
[x] the link to the wiki for dev instructions probably should be the link to the hack/ folder
[x] the link to the code review refers to a specific commit - here is a more general link
[x] do we still use Travis for CI?
[x] pretty sure we want the Python 3 version of unittest

For Artefactual use:

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[ ] All pull requests related to this issue are properly linked
[ ] All pull requests related to this issue have been merged
[ ] Details about this issue have been added to the release notes (if applicable)

archivematica / Issues

Problem: CONTRIBUTING.md does not reflect current workflow #1671