Properly document jgvariant-ostree.

Change-Id: I0aa3b1df512ef99d0e25d73efdd34a1b488e7d0d
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Summary.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Summary.java
index 8f4ddf6..bc94436 100644
--- a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Summary.java
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Summary.java
@@ -11,11 +11,29 @@
  * <p>Stored as a file named {@code summary} in the OSTree repository root.
  *
  * <p>Reference: {@code ostree-core.h#OSTREE_SUMMARY_GVARIANT_STRING}
+ *
+ * @param entries an entry in the summary file.
+ * @param metadata additional keys and values contained in the summary.
  */
 public record Summary(List<Entry> entries, Metadata metadata) {
 
+  /**
+   * An entry in the summary file of an OSTree repository, describing a ref.
+   *
+   * @param ref a ref name.
+   * @param value data describing the ref.
+   */
   public record Entry(String ref, Value value) {
 
+    /**
+     * The value part of an entry in the summary file of an OSTree repository.
+     *
+     * <p>Describes the {@link Commit} currently named by the corresponding ref.
+     *
+     * @param size the size of the commit.
+     * @param checksum the checksum of the commit.
+     * @param metadata additional metadata describing the commit.
+     */
     public record Value(long size, Checksum checksum, Metadata metadata) {
 
       private static final Decoder<Value> DECODER =
@@ -25,6 +43,11 @@
               Checksum.decoder(),
               Metadata.decoder());
 
+      /**
+       * Acquires a {@link Decoder} for the enclosing type.
+       *
+       * @return a possibly shared {@link Decoder}.
+       */
       public static Decoder<Value> decoder() {
         return DECODER;
       }
@@ -33,6 +56,11 @@
     private static final Decoder<Entry> DECODER =
         Decoder.ofStructure(Entry.class, Decoder.ofString(StandardCharsets.UTF_8), Value.decoder());
 
+    /**
+     * Acquires a {@link Decoder} for the enclosing type.
+     *
+     * @return a possibly shared {@link Decoder}.
+     */
     public static Decoder<Entry> decoder() {
       return DECODER;
     }
@@ -41,6 +69,11 @@
   private static final Decoder<Summary> DECODER =
       Decoder.ofStructure(Summary.class, Decoder.ofArray(Entry.decoder()), Metadata.decoder());
 
+  /**
+   * Acquires a {@link Decoder} for the enclosing type.
+   *
+   * @return a possibly shared {@link Decoder}.
+   */
   public static Decoder<Summary> decoder() {
     return DECODER;
   }