bitbake-user-manual-metadata.xml: Added [eventmask] flag information.

Reported-by: Laszlo Papp <lpapp@kde.org>
Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
bitbake-user-manual-metadata.xml: Updated do_package_write example

Given that the "do_package_write" task doesn't exist in OE anymore,
steal another, existing example to demonstrate the "rdeptask" flag.

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