[goffice] Added a comment about what are drop bars. [#630796]

[Jean Bréfort <jbrefort src gnome org>]

commit d4e5834835f7334f24307e94fa4b62f25d08db69
Author: Jean Brefort <jean brefort normalesup org>
Date:   Sun Oct 3 15:14:37 2010 +0200

    Added a comment about what are drop bars. [#630796]

 plugins/plot_barcol/plot-types.xml.in |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/plugins/plot_barcol/plot-types.xml.in b/plugins/plot_barcol/plot-types.xml.in
index 95c235d..c9e119e 100644
--- a/plugins/plot_barcol/plot-types.xml.in
+++ b/plugins/plot_barcol/plot-types.xml.in
@@ -174,6 +174,9 @@
 		<property name="guru-hints">backplane</property>
 	</Type>
 
+	<!-- Drop bars are bars goint from an initial position
+	to a final position; the fill color is inverted when final position is lower
+	than the initial position; they may be used in stock plots. -->
 	<Type _name="Horizontal Drop Bars" row="1" col="2"
 		engine="GogDropBarPlot" family="DropBar"
 		_description="Horizontal drop bars."