[gtk+] Scrollbar: Tweak intro docs a bit

[Daniel Boles <dboles src gnome org>]

commit 874b03e4fe62c711385255c147778a8db036fc48
Author: Daniel Boles <dboles src gnome org>
Date:   Mon Mar 20 23:54:57 2017 +0000

    Scrollbar: Tweak intro docs a bit
    
    Explain where the adjustment comes from, clarify some of the wording
    about how its fields influence the scrollbar, and also note that the
    steppers may not be present, since they aren’t in our default themes.

 gtk/gtkscrollbar.c |   19 +++++++++----------
 1 files changed, 9 insertions(+), 10 deletions(-)
---
diff --git a/gtk/gtkscrollbar.c b/gtk/gtkscrollbar.c
index b51a587..b09bf13 100644
--- a/gtk/gtkscrollbar.c
+++ b/gtk/gtkscrollbar.c
@@ -43,16 +43,15 @@
  * The #GtkScrollbar widget is a horizontal or vertical scrollbar,
  * depending on the value of the #GtkOrientable:orientation property.
  *
- * The position of the thumb in a scrollbar is controlled by the scroll
- * adjustments. See #GtkAdjustment for the fields in an adjustment - for
- * #GtkScrollbar, the #GtkAdjustment:value field represents the position
- * of the scrollbar, which must be between the #GtkAdjustment:lower field
- * and #GtkAdjustment:upper - #GtkAdjustment:page-size. The
- * #GtkAdjustment:page-size field represents the size of the visible
- * scrollable area. The #GtkAdjustment:step-increment and
- * #GtkAdjustment:page-increment fields are properties when the user asks to
- * step down (using the small stepper arrows) or page down (using for
- * example the `Page Down` key).
+ * Its position and movement are controlled by the adjustment that is passed to
+ * or created by gtk_scrollbar_new(). See #GtkAdjustment for more details. The
+ * #GtkAdjustment:value field sets the position of the thumb and must be between
+ * #GtkAdjustment:lower and #GtkAdjustment:upper - #GtkAdjustment:page-size. The
+ * #GtkAdjustment:page-size represents the size of the visible scrollable area.
+ * The fields #GtkAdjustment:step-increment and #GtkAdjustment:page-increment
+ * fields are added or subtracted to the #GtkAdjustment:value when the user asks
+ * to move by a step (using e.g. the cursor arrow keys or, if present, the
+ * stepper buttons) or by a page (using e.g. the Page Down/Up keys).
  *
  * # CSS nodes
  *