docs: Add traling docs to aliases

Author: dangotbanned

narwhals/_compliant/typing.py

@@ -112,8 +112,18 @@
 LazyExprT_contra = TypeVar("LazyExprT_contra", bound=LazyExprAny, contravariant=True)
 
 AliasNames: TypeAlias = Callable[[Sequence[str]], Sequence[str]]
+"""A function aliasing a *sequence* of column names."""
+
 AliasName: TypeAlias = Callable[[str], str]
+"""A function aliasing a *single* column name."""
+
 EvalSeries: TypeAlias = Callable[
     [CompliantFrameT], Sequence[CompliantSeriesOrNativeExprT]
 ]
+"""A function from a `Frame` to a sequence of `Series`*.
+
+See [underwater unicorn magic](https://narwhals-dev.github.io/narwhals/how_it_works/).
+"""
+
 EvalNames: TypeAlias = Callable[[CompliantFrameT], Sequence[str]]
+"""**NEEDS DOC**"""