sdk-manual: Added a red-text "role" to the style sheet.

This allows you to use the following to make a paragraph display
using red-colored text:

  <para role='writernotes'>Here is the sentence.</para>

What this allows is to create areas in the manual that are
easily identified as questions to the reviewers.

(From yocto-docs rev: 007ea508a36f453c66970666490a82885a8749e1)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/sdk-manual/sdk-style.css

@@ -685,6 +685,10 @@ hr {
   background-color: #f0f0f2;
 }
 
+.writernotes {
+  color: #ff0000;
+}
+
 .glossary dl dt,
 .variablelist dl dt,
 .variablelist dl dt span.term {