Adding downloadables removes comments from `server.toml`

[Newtbytes]

Example diff after adding Just Player Heads with mcman add modrinth:

- # MARK: Head Drops
[[mods]]
type = "modrinth"
id = "just-mob-heads"
version = "hbgvhaSJ"

+ [[mods]]
+ type = "modrinth"
+ id = "just-player-heads"
+ version = "kIVhv3YU"

It would be more convenient if mcman add/mcman import/etc. added mods while doing absolutely nothing else. I assume this is because its parsing the file into some data structure, adding the mod to the data structure, and writing it back with no consideration for concrete syntax.