feat: node types readme

Author: prestwich

crates/node-types/README.md

@@ -0,0 +1,10 @@
+# Signet Node Types
+
+This crate provides parameterizations and conveneniences for the Signet node's
+use of reth's internal generics. E.g. [`NodePrimitives`] and [`NodeTypes`].
+
+It also provides a [`NodeTypesDbTrait`] to aggregate several trait constraints
+on the database type. This is then used in the node and in `signet-db`.
+
+This crate is mostly shims. It is not intended to be used outside of the
+Signet node and `signet-db` crates.