patch 9.1.0868: the warning about missing clipboard can be improved

Problem:  the warning about missing clipboard can be improved
          (after v9.1.0852)
Solution: use different warnings depending on whether or not clipboard
          support is included in Vim, update related documentation

Improve the Warnings about missing clipboard registers

- Make it translatable
- Use a different warning, when clipboard support was not compiled in
- add a reference to :h W24
- explain in more detail the error message

closes: #16069

Signed-off-by: Christian Brabandt <cb@256bit.org>

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    868,
 /**/
     867,
 /**/