Document some of our client classes

This is mostly aiming to give an overview rather than be anything
comprehensive (there's another 230+ undocumented classes to go :p), but
it's a start.

Mostly just an excuse for me to procrastinate working on the nasty bugs
though!

projects/fabric/src/client/java/dan200/computercraft/client/model/turtle/TurtleModel.java

@@ -17,6 +17,11 @@ import javax.annotation.Nullable;
 import java.util.HashMap;
 import java.util.Map;
 
+/**
+ * The custom model for turtle items, which renders tools and overlays as part of the model.
+ *
+ * @see TurtleModelParts
+ */
 public class TurtleModel extends ForwardingBakedModel {
     private final TurtleModelParts parts;
 

projects/fabric/src/client/java/dan200/computercraft/client/model/turtle/TurtleModelLoader.java

@@ -19,6 +19,12 @@ import java.util.List;
 import java.util.Objects;
 import java.util.function.Function;
 
+/**
+ * A model "loader" (the concept doesn't quite exist in the same way as it does on Forge) for turtle item models.
+ * <p>
+ * This reads in the associated model file (typically {@code computercraft:block/turtle_xxx}) and wraps it in a
+ * {@link TurtleModel}.
+ */
 public final class TurtleModelLoader {
     private static final ResourceLocation COLOUR_TURTLE_MODEL = new ResourceLocation(ComputerCraftAPI.MOD_ID, "block/turtle_colour");