poky/.git/.gitignore: added the yocto-project-kernel-manual.pdf file

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>

.gitignore

@@ -31,4 +31,8 @@ documentation/yocto-project-qs/yocto-project-qs.html
 documentation/yocto-project-qs/yocto-project-qs.tgz
 documentation/kernel-manual/yocto-project-kernel-manual.html
 documentation/kernel-manual/yocto-project-kernel-manual.tgz
+documentation/kernel-manual/yocto-project-kernel-manual.pdf
+documentation/kernel-manual/yocto-project-kernel-manual.tgz
+
+