[css-color-5][editorial] Update changes since 15 Dec WD

Author: svgeesus

css-color-5/Overview.bs

@@ -2776,6 +2776,19 @@ to WCAG 2.1 <a href="https://www.w3.org/TR/WCAG21/#contrast-minimum">section 1.4
 Changes {#changes}
 =======
 
+<h3 id="changes-20211215">Since the <a href="https://www.w3.org/TR/2021/WD-css-color-5-20211215/">Working Draft of 15 December 2021</a></h3>
+
+<ul>
+	<!-- to 27 Feb 2022 -->
+	<li>Clearly described potential clash of component names with named constants such as PI</li>
+	<li>Clarified that Relative Color Syntax does not use legacy (comma-separated) syntax</li>
+	<li>Corrected grammar of the rgb() function, 'none' was not listed as an option for alpha</li>
+	<li>Changed serialization of color-mix() which uses hsl or hwb, to maximise precision</li>
+	<li>Added an out of gamut color-mix example</li>
+	<li>Use the term "cannot express the color" to describe HSL and HWB models which cannot represent extended, out of gamut colors.</li>
+	<li>Fixed some spelling errors</li>
+</ul>
+
 <h3 id="changes-20210601">Since the <a href="https://www.w3.org/TR/2021/WD-css-color-5-20210601/">Working Draft of 1 June 2021</a></h3>
 
 <ul>