Add some docs.

lib/gallery-context.tsx

@@ -1,19 +1,60 @@
 import React from "react";
 
 export type GalleryComposition = {
+  /** A unique identifier/primary key for the composition. */
   id: string;
+
+  /** The type of composition. */
   kind: "creature" | "mandala";
-  owner: string;
-  ownerName: string;
-  title: string;
+
+  /**
+   * The serialized value of the composition. This
+   * is interpreted differently based on the composition
+   * type.
+   */
   serializedValue: string;
+
+  /** The user ID of the user who submitted the composition. */
+  owner: string;
+
+  /**
+   * The name of the user who submitted the composition.
+   */
+  ownerName: string;
+
+  /** The title of the composition. */
+  title: string;
 };
 
+/**
+ * A generic interface for interacting with the gallery.
+ */
 export interface GalleryContext {
+  /**
+   * All the compositions in the gallery that have been loaded
+   * from the network.
+   */
   compositions: GalleryComposition[];
+
+  /** Whether we're currently loading the gallery from the network. */
   isLoading: boolean;
+
+  /** If a network error occurred, this is it. */
   error?: string;
+
+  /**
+   * Attempt to refresh the gallery from the network. Return whether
+   * the request was accepted (if we're already loading the gallery, or
+   * if a prequisite service hasn't been initialized yet, this can
+   * return `false`).
+   */
   refresh(): boolean;
+
+  /**
+   * The timestamp (milliseconds since 1970) of the last time
+   * the gallery data was refreshed. If it has never been loaded,
+   * this will be 0.
+   */
   lastRefresh: number;
 }