meta-poky: update conf-notes.txt

Now suggesting to run 'runqemu qemux86-64',
aligning with conf-notes.txt in openembedded-core

'runqemu qemux86' doesn't work any more.
The "Quick Build" documentation has already been updated
but not this message that we get when sourcing "oe-init-build-env"

(From meta-yocto rev: d0d39a9057b3da3de339b8fa81545be9800478e8)

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-poky/conf/conf-notes.txt

@@ -11,7 +11,7 @@ Common targets are:
     meta-toolchain
     meta-ide-support
 
-You can also run generated qemu images with a command like 'runqemu qemux86'
+You can also run generated qemu images with a command like 'runqemu qemux86-64'.
 
 Other commonly useful commands are:
  - 'devtool' and 'recipetool' handle common recipe tasks