[PATCH 1/4] rcutorture/doc: Add a new way to create initrd using dracut

Using dracut is another way to get an initramfs for kvm based rcu torture tests, which is more flexible than using the host's initramfs image, because modules and binaries may be added or removed via dracut command options. So add an example in the document, in case that there are some situations

[PATCH 1/4] rcutorture/doc: Add a new way to create initrd using dracut

Using dracut is another way to get an initramfs for kvm based rcu torture tests, which is more flexible than using the host's initramfs image, because modules and binaries may be added or removed via dracut command options. So add an example in the document, in case that there are some situations