bitbake: bitbake-user-manual-style.css: Added permalink style for display

Fixes [YOCTO #5772]

Added a couple styles to the CSS style sheet so that the displayed
permalink symbol is barely visible unless you hover over it with
the mouse.

(Bitbake rev: ee8db0cda1c8716ab0151a4859bfff84b2f3bd58)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/doc/bitbake-user-manual/bitbake-user-manual-style.css

@@ -313,6 +313,13 @@ a:hover {
   /*font-weight: bold;*/
 }
 
+/* This style defines how the permalink character
+   appears by itself and when hovered over with
+   the mouse. */
+
+[alt='Permalink'] { color: #eee; }
+[alt='Permalink']:hover { color: black; }
+
 
 div.informalfigure,
 div.informalexample,