[gegl] docs: document relative units for gegl-chain

[Øyvind Kolås <ok src gnome org>]

commit 7c74925680a27c85268274e3381f876d2002b865
Author: Øyvind Kolås <pippin gimp org>
Date:   Thu Apr 20 00:04:53 2017 +0200

    docs: document relative units for gegl-chain

 docs/gegl-chain.txt |   11 ++++++++++-
 1 files changed, 10 insertions(+), 1 deletions(-)
---
diff --git a/docs/gegl-chain.txt b/docs/gegl-chain.txt
index 9a87e31..bb43641 100644
--- a/docs/gegl-chain.txt
+++ b/docs/gegl-chain.txt
@@ -22,7 +22,9 @@ property assignment for the preceding operation. For example:
 If you try to assign a property that doesn't exist, the error message will
 contain a list of valid properties for the operation.
 
-The format treats input and output pads as explicitly linked when they follow each other, to create a 
sub-chain hooked up to an aux input assign the aux pad with the sub chain contained in square brackets, like 
this:
+The format treats input and output pads as explicitly linked when they follow
+each other, to create a sub-chain hooked up to an aux input assign the aux pad
+with the sub chain contained in square brackets, like this:
 
  $ gegl in.jpg -- noise-reduction iterations=2 over aux=[ text string='hello there' color=white size=32 
translate x=100 y=100 dropshadow radius=2 x=1.5 y=1.5 ]
 
@@ -31,6 +33,13 @@ creating masks for color adjustments based on image content, for instance the
 following example, which uses a blurred version of an image as a threshold mask
 - which thus becomes a local content dependent thresholding filter.
 
+ $ gegl in.jpg -- id=a threshold aux=[ ref=a gaussian-blur std-dev-x=120 std-dev-y=120 ]
+
+When it is more reasonable to specify dimensions relative to the height of an
+image - similar to CSS vh dimensions, GEGL can use a "rel" suffix similar to
+the CSS vh unit, on the commandline and in other tools, a scaling factor to
+scale "rel" units is passed with the parsing API.
+
  $ gegl in.jpg -- id=a threshold aux=[ ref=a gaussian-blur std-dev-x=0.1rel std-dev-y=0.1rel ]
 
 If gegl have working gegl:ff-load and gegl:ff-save ops, The gegl binary also