[devhelp] Sidebar: improve a comment

[Sébastien Wilmet <swilmet src gnome org>]

commit 2190b9cd535fd5f1a62bcfc8f866b85da4c9c722
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Sun Jan 21 13:24:21 2018 +0100

    Sidebar: improve a comment

 src/dh-sidebar.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/src/dh-sidebar.c b/src/dh-sidebar.c
index 78cdce5..19ceae8 100644
--- a/src/dh-sidebar.c
+++ b/src/dh-sidebar.c
@@ -137,8 +137,9 @@ search_idle_cb (gpointer user_data)
         book_id = book_link != NULL ? dh_link_get_book_id (book_link) : NULL;
 
         /* Disconnect the model during the filter, for:
-         * 1. better performances.
-         * 2. clearing the selection.
+         * 1. Better performances.
+         * 2. Clearing the selection.
+         * 3. Because it's required by dh_keyword_model_filter().
          */
         gtk_tree_view_set_model (priv->hitlist_view, NULL);