bitbake: gitignore: Update for recent docs changes

Added a few more files to gitignore file to allow document
generation testing.

(Bitbake rev: f6310ca9ccb402a7569a79a4e92751c6d5733697)

Signed-off-by: Bill Traynor <wmat@alphatroop.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

.gitignore

@@ -17,8 +17,7 @@ hob-image-*.bb
 !meta-yocto
 !meta-yocto-bsp
 !meta-yocto-imported
-bitbake/doc/manual/html/
-bitbake/doc/manual/pdf/
-bitbake/doc/manual/txt/
-bitbake/doc/manual/xhtml/
+documentation/user-manual/user-manual.html
+documentation/user-manual/user-manual.pdf
+documentation/user-manual/user-manual.tgz
 pull-*/