doc(interface-types) Improve module descriptions.

lib/interface-types/src/ast.rs

@@ -1,3 +1,6 @@
+//! Represents the WIT language as a tree. This is the central
+//! representation of the language.
+
 use crate::interpreter::Instruction;
 use std::str;
 

lib/interface-types/src/decoders/mod.rs

@@ -1 +1,4 @@
+//! Reads the AST from a particular data representation; for instance,
+//! `decoders::binary` reads the AST from a binary.
+
 pub mod binary;

lib/interface-types/src/encoders/mod.rs

@@ -1 +1,5 @@
+//! Writes the AST into a particular format; for instance,
+//! `encoders::wat` writes the AST into a string representing WIT with
+//! its textual format.
+
 pub mod wat;

lib/interface-types/src/interpreter/mod.rs

@@ -1,3 +1,5 @@
+//! A stack-based interpreter to execute instructions of WIT adapters.
+
 mod instruction;
 mod instructions;
 pub mod stack;