document hashtag subscription

docs/activitypub.7

@@ -91,8 +91,11 @@ Supported with share semantics.
 Supported.
 Primarily used to acknowledge replies and complete threads, without
 additional semantics.
+.It Vt Add
+Works with collections.
 .It Vt Follow
 Supported.
+Can follow both actors and collections.
 .Vt Accept
 and
 .Vt Undo

docs/honk.1

@@ -50,7 +50,6 @@ Examples:
 .Dl @user@example.social
 .Dl https://example.social/users/user
 .Pp
-.Pp
 Fellow honkers may be added to one or more
 .Ic combos
 to suit one's organizational preferences.
@@ -64,6 +63,13 @@ will exclude a honker's posts from the primary feed.
 It is also possible to skip subscribing.
 In this case, regular posts are not received, but replies and posts fetched
 via other means will appear in the relevant combos.
+.Pp
+In addition to honkers, it is possible to subscribe to a hashtag collection.
+(Where supported.)
+Enter the collection URL as the honker URL.
+.Pp
+Separately, hashtags may be added to a combo by creating a honker with a url
+of the desired hashtag (including #).
 .Ss Viewing
 The primary feed is accessed via the
 .Pa home