fix: README formatting

README.md

@@ -10,7 +10,7 @@ private configuration that may be useful to other people.
 A list of XMPP servers that are uncooperative in regards to spam.
 Blacklist stored at `$out/blacklist.txt`.
 
-(Source link.)[https://github.com/JabberSPAM/blacklist]
+[Source link.](https://github.com/JabberSPAM/blacklist)
 
 ## License