Same way you link any other site to any other account...
You sign up to the first site creating login details for the host site be it Inara or EDSM or any other ED site..
Putting in the Email and password you want to to make the site account...
Then once the primary site account is made you literarly click on the BIG import data buttons on the site which imports data...
After hitting the great big button your asked to select which game service provider PC ,XBOX, PSN you want to link to the site you on in that browser ...
You then put in the account details for that providers networks Fdev game and then wait for the site server to exctract the data from Fdev server CAPI system...
Yes it it that easy ... its so easy that the site don't even bother with a how too... just chuck up the login screens each time...