Your e-mail daemon should already have configuration for DKIM, and the same tool that generates that key should also print out the complete DNS entry you need. Configuring DKIM in your daemon is a bit of work; The DNS portion of it is simple.
If a person is trying to self-host their own MX and doesn't want to get into the details of configuring SPF, DKIM and DMARC, I would highly recomment they go with something like gsuite or office365 instead. Or some other managed email hosting provider that will do the DKIM setup for them.