feat: flake github:jj-vcs/jj (#1019)

Author: Malix-Labs

flakes/manual.toml

@@ -89,6 +89,11 @@ type = "github"
 owner = "input-output-hk"
 repo = "haskell.nix"
 
+[[sources]]
+type = "github"
+owner = "jj-vcs"
+repo = "jj"
+
 [[sources]]
 type = "github"
 owner = "jonahbron"