[gimp-web/testing] Add 'Parametric Brush' tutorial to index list

[Pat David <patdavid src gnome org>]

commit f05cc9b49e2356263948da2e07386b5eba9ca67a
Author: Pat David <patdavid gmail com>
Date:   Thu Jul 19 13:22:22 2018 -0500

    Add 'Parametric Brush' tutorial to index list

 content/tutorials/index.md | 8 ++++++++
 1 file changed, 8 insertions(+)
---
diff --git a/content/tutorials/index.md b/content/tutorials/index.md
index 429c0ea9..e8620407 100644
--- a/content/tutorials/index.md
+++ b/content/tutorials/index.md
@@ -61,6 +61,14 @@ Layer masking and creative filter applications.
 [Focus Group]: {filename}Focus_Group/index.md
 
 
+## Painting
+
+[Parametric Brushes][]  
+A look at the advantages and flexibility of using Parametric Brushes.
+
+[Parametric Brushes]: {filename}Parametric_Brush/index.md
+
+
 ## Programming
 
 [Basic GIMP Perl][]