Download your preferred iso image from http://www.android-x86.org/
Create storage file:
qemu-img create -f qcow2 android_marshmellow.img 20G
Install using virt manager making sure to use the iso and the storage created in the previous steps.
Select NO when prompted to use GPT.
Create a new partition and make sure to set the newly created partition as bootable.
Continue the installation and reboot when given the option.
http://www.android-x86.org/documents/qemuhowto