You don’t need the whole repo, you can just download the artifacts (rpms) from there and install them.
But to answer your question, you can use the
zypper) tool to manage repositories:
ssu ar <reponame> https://path/to/repository # add a repo
ssu dr <reponame> # disable a repo but leave configured
ssu er <reponame> # enable a disabled repo
ssu rr <reponame> # remove a repo
All these work as regular user.
After adding you have to
pkcon refresh (or
zypper re) to update the package index.
You can use any
reponame you want, but the URL must point to an actual rpm repo (it has to have a certain structure and index files), can’t be just any url. I think in this case that would be
http://repo.merproject.org/obs/home:/nielnielsen/sailfish_latest_armv7hl/ but I haven’t tested.
Also NB: Adding any repositories can be very dangerous as the contents of the repos might conflict or replace system packages. Be very careful with that.