Install Yarn on openSUSE.md

Following the official guide, you'll bump into the following error:

$ sudo zypper ref
Repository 'Google-Chrome' is up to date.
Retrieving repository 'Yarn' metadata --------------------------------------------------------------------------------------------------------------------------------------------------------------------------[\]
Warning: File 'repomd.xml' from repository 'Yarn' is signed with an unknown key '9CBBB5586963F07F'.

    Note: Signing data enables the recipient to verify that no modifications occurred after the data
    were signed. Accepting data with no, wrong or unknown signature can lead to a corrupted system
    and in extreme cases even to a system compromise.

    Note: File 'repomd.xml' is the repositories master index file. It ensures the integrity of the
    whole repo.

    Warning: We can't verify that no one meddled with this file, so it might not be trustworthy
    anymore! You should not continue unless you know it's safe.

File 'repomd.xml' from repository 'Yarn' is signed with an unknown key '9CBBB5586963F07F'. Continue? [yes/no] (no):

To avoid this error, you need to add the key used for sining the Yarn repository. I don't know why they don't refer to the key in the section for openSUSE, but the key is stored here.

$ wget https://dl.yarnpkg.com/rpm/pubkey.gpg
$ sudo rpm --import pubkey.gpg

To sum up, the whole step will be:

$ sudo zypper ar -f https://dl.yarnpkg.com/rpm/ Yarn
$ wget https://dl.yarnpkg.com/rpm/pubkey.gpg
$ sudo rpm --import pubkey.gpg
$ sudo zypper ref
$ sudo zypper in yarn