humans.txt

TL;DR

humans.txt is a simple text file that can sometimes be found in the root of a website, with the simple role of acknowledging the people who have worked on it. It does not interfere with the code of the website and can cause no malfunctions.  

Do websites need a humans.txt file?

No, they do not. It is not a requirement in any way. It is just a way of expressing appreciation for the team behind the creation of tje website. humans.txt is a simple text file that you can place in the root of a website.

How can it be created and used?

Detailed instructions on how it can be used can be found on http://humanstxt.org/Standard.html. They involve creating a simple .txt file and linking it in the website header using this author tag:
<link rel="author" href="humans.txt" />. It is recommended to include the name and role of every person involved in the project, whether a developer, designer, content creator, SEO specialist or webmaster. Contact details may be added, but these could also be used by spammers.

If you operate your website using a CMS and do not have access to the root of the website and lack permissions to upload files, then you cannot acknowledge the team in this way.