[css-images-4] Add a placeholder issue for the stripes() function.

Author: tabatkins

css-images-4/Overview.bs

@@ -48,8 +48,8 @@ Introduction {#intro}
    ██ ████ ██     ██ ██     ██  ██████   ████████ ██
 -->
 
-Image Values: the <<image>> type {#image-values}
-=================================================
+2D Image Values: the <<image>> type {#image-values}
+===================================================
 
 The <<image>> value type denotes a 2D image. It can be a
 	<a section href="#url-notation">url reference</a>,
@@ -1577,6 +1577,14 @@ Gradient Color-Stops</h3>
 	have identical results whether the color interpolation is done in premultiplied or non-premultiplied color-space.
 	Differences only arise when both the color and transparency differ between the two endpoints.
 
+
+1D Image Values: the ''stripes()'' notation {#stripes}
+======================================================
+
+	Issue: <a href="https://github.com/w3c/csswg-drafts/issues/2532">Per WG resolution</a>,
+	define the ''stripes()'' function
+	which creates a 1D image for use in borders/outlines.
+
 <!--
  ██████  ████ ████████ ████ ██    ██  ██████
 ██    ██  ██       ██   ██  ███   ██ ██    ██