README: Add module overview.

Change-Id: I8c4701e8d4561940025165dd3beb448e3443de36
diff --git a/README.md b/README.md
index 39d39e3..f1a2d05 100644
--- a/README.md
+++ b/README.md
@@ -5,13 +5,16 @@
 
 ## Overview
 
-Instances of `Decoder<T>` read a given type of GVariant-encoded value
-from a [ByteBuffer][].  The class also contains factory methods to
-acquire those instances.
+`jgvariant-core` provides `Decoder<T>`, which read a given type of
+GVariant-encoded value from a [ByteBuffer][].  The class also contains
+factory methods to acquire those instances.
 
 The various subclasses of `Decoder` together implement the [GVariant
 serialization][] specification.
 
+`jgvariant-ostree` provides instances of `Decoder<T>` for various
+[GVariant][] types used in [OSTree][] repositories.
+
 
 ## Example
 
@@ -89,4 +92,5 @@
 [ByteBuffer]: https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/nio/ByteBuffer.html
 [GVariant]: https://docs.gtk.org/glib/struct.Variant.html
 [GVariant serialization]: https://people.gnome.org/~desrt/gvariant-serialisation.pdf
+[OSTree]: https://ostreedev.github.io/ostree/
 [String]: https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html
diff --git a/jgvariant-ostree/src/main/java/module-info.java b/jgvariant-ostree/src/main/java/module-info.java
index e51c586..4a59152 100644
--- a/jgvariant-ostree/src/main/java/module-info.java
+++ b/jgvariant-ostree/src/main/java/module-info.java
@@ -1,6 +1,5 @@
 /**
- * Provides a parser for the <a href="https://docs.gtk.org/glib/struct.Variant.html">GVariant</a>
- * serialization format.
+ * {@link eu.mulk.jgvariant.core.Decoder} instances for OSTree repositories.
  *
  * <ul>
  *   <li><a href="#sect-overview">Overview</a>