Just use regular line breaks.
"This is line 1
This is line 2
This is line 3"
Be aware, that it will shrink the text to fit the window, so if you put a huge amount of stuff in there, it will end up really small.
Also, fun fact. You can use color codes as well.
"[0F52BA] Please read the /rules before gaming on this server. Not knowing is not an excuse! [-]"
First []s creates the color, the [-] ends it. Use regular HTML color codes.