make more clear what is meant

Author: tshepang

src/ty-fold.md

@@ -1,6 +1,6 @@
 # `TypeFoldable` and `TypeFolder`
 
-In [a previous chapter], we discussed instantiating binders. This involves looking at everything inside of a `Early/Binder`
+In [a previous chapter], we discussed instantiating binders. This involves looking at everything inside of a `Early(Binder)`
 to find any usages of the bound vars in order to replace them. Binders can wrap an arbitrary Rust type `T` not just a `Ty` so
 how do we implement the `instantiate` methods on the `Early/Binder` types.