[fanbox] add 'comments' option, extend 'metadata' option (#6287)

docs/configuration.rst

@@ -2312,6 +2312,19 @@ Description
     * ``"hitomi"``:  Download the corresponding gallery from ``hitomi.la``
 
 
+extractor.fanbox.comments
+-------------------------
+Type
+    ``bool``
+Default
+    ``false``
+Description
+    Extract ``comments`` metadata.
+
+    Note: This requires 1 or more additional API requests per post,
+    depending on the number of comments.
+
+
 extractor.fanbox.embeds
 -----------------------
 Type
@@ -2338,11 +2351,20 @@ Type
 Default
     ``false``
 Example
-    * ``user,plan``
-    * ``["user", "plan"]``
+    * ``user,plan,comments``
+    * ``["user", "plan", "comments"]``
 Description
     Extract ``plan`` and extended ``user`` metadata.
 
+    Supported fields when selecting which data to extract are
+
+    * ``comments``
+    * ``plan``
+    * ``user``
+
+    Note: ``comments`` can also be enabled via
+    `fanbox.comments <extractor.fanbox.comments_>`__
+
 
 extractor.flickr.access-token & .access-token-secret
 ----------------------------------------------------