docs: improve srcery_bg description

Closes #109
Thanks @Dorovich

README.md

@@ -295,17 +295,19 @@ Default: 0
 
 #### g:srcery\_bg
 
-Default: `[g:srcery_black, 0]`
-
 Let's you customize the background color. This var takes a list with two
-elements, with a HEX in the first position, and a terminal color index for the
-second position. This lets you set both a 24-bit color, and a 8bit terminal
+values, with a quoted HEX in the first position, and a terminal color index for
+the second position. This lets you set both a 24-bit color, and a 8bit terminal
 color index.
 
-You can specify `NONE` as a value, which would be the same as the previous
-option `srcery_bg_passthrough`
+You can specify `'NONE'` as one of the values to make it transparent, as such
+`['NONE', 'NONE']` would be the same as the previous option
+`g:srcery_bg_passthrough = 1`.
 
-You can specify `DEFAULT` as a value, if you only want to customize one value.
+You can specify `'DEFAULT'` as one of the values in order to use that
+position's default value.
+
+Default: `[g:srcery_black, 0]`
 
 #### g:srcery\_hard\_black\_terminal\_bg
 

doc/srcery.txt

@@ -237,15 +237,17 @@ g:srcery_italic_types
 g:srcery_bg
 
 	Let's you customize the background color. This var takes a list with
-	two elements, with a HEX in the first position, and a terminal color
-	index for the second position. This lets you set both a 24-bit color,
-	and a 8bit terminal color index.
+	two values, with a quoted HEX in the first position, and a terminal
+	color index for the second position. This lets you set both a 24-bit
+	color, and a 8bit terminal color index.
 
-	You can specify `NONE` as a value, which would be the same as the
-	previous option `srcery_bg_passthrough`
+	You can specify `'NONE'` as one of the values to make it transparent,
+	as such `['NONE', 'NONE']` would be the same as the previous option
+	`g:srcery_bg_passthrough = 1`.
 
-	You can specify `DEFAULT` as a value, if you only want to customize
-	one value.
+
+	You can specify `'DEFAULT'` as one of the values in order to use that
+	position's default value.
 
 	Default: `[g:srcery_black, 0]`