docs: update affiliation for tuunit

[tuunit]

Should I update github_users.json and the email-map files as well? This isn't clear from the README.

It states:

Only the Developers affiliations list dev1, dev2, dev3, dev4, dev5, ... should be edited manually.

but a paragraph later it also states:

Other files used for affiliations are the email map file and github users file.

[lukaszgryglicki]

/lgtm