[css-fonts-4] Add note on historical reasons for the serif and sans-serif generics w3c#5053

Author: svgeesus

css-fonts-4/Overview.bs

@@ -467,6 +467,17 @@ Generic font families</h4>
 	        Serif fonts are typically proportionately-spaced.
 	        They often display a greater variation between thick and thin strokes
 	        than fonts from the ''sans-serif'' generic font family.
+
+			Note: ''serif'' and ''sans-serif''
+			only apply to a small handful of writing scripts. 
+			Their use as generic font families in CSS is historical, 
+			and reflects the Latin-centric nature
+			of early Web development.
+			Better and more widely applicable names would have been,
+			for example, "modulated" and "monoline".
+			However, for reasons of Web compatibility,
+			these names cannot be changed.
+
 	        CSS uses the term "serif" to apply to a font for any script,
 	        although other names might be more familiar for particular scripts,
 	        such as Mincho (Japanese),
@@ -479,8 +490,7 @@ Generic font families</h4>
 
 	        ''serif'' must always map to at least one matched font face.
 
-	        Note: ''serif'' must always map to at least one matched font face.
-	        However, no guarantee is placed on the character coverage of that font
+	        Note: No guarantee is placed on the character coverage of that font
 	        face. Therefore, the font ''serif'' is mapped to may not end up being
 	        used for all content.