Change WTFPL to MIT (part 3)

Relicense WTFPL media to CC BY-SA 3.0.
Various corrections and edits.

mods/boats/README.txt

@@ -4,9 +4,12 @@ See license.txt for license information.
 
 Authors of source code
 ----------------------
-PilzAdam (MIT)
+Originally by PilzAdam (MIT)
+Various Minetest developers and contributors (MIT)
 
 Authors of media (textures and model)
 -------------------------------------
-Textures: Zeg9 (MIT)
-Model: thetoon and Zeg9 (MIT), modified by PavelS(SokolovPavel) (MIT)
+Textures: Zeg9 (CC BY-SA 3.0)
+Model: thetoon and Zeg9 (CC BY-SA 3.0),
+  modified by PavelS(SokolovPavel) (CC BY-SA 3.0),
+  modified by sofar (CC BY-SA 3.0)