Import installation instructions inside an existing system

Copy documentation from installing inside an existing system from

https://pagure.io/fork/walters/workstation-ostree-config/branch/f24-continuous

README.md

@@ -45,6 +45,73 @@ Important issues:
  - [Anaconda autopartitoning](https://github.com/rhinstaller/anaconda/issues/800) - be sure to use `/var/home` instead of `/home`
  - [flatpak system repo](https://github.com/flatpak/flatpak/issues/113#issuecomment-247022006)
 
+Installing *inside* an existing system
+---------------------------------------
+
+A really neat feature of OSTree is that you can
+*parallel install* inside your existing OS.  Let's try that, we
+first make sure we have the ostree packages:
+
+```
+yum -y install ostree ostree-grub2
+```
+
+Next, we add `/ostree/repo` to the filesystem:
+```
+ostree admin init-fs /
+```
+
+Add a remote which points to the CentOS CI content:
+```
+ostree remote add --set=gpg-verify=false fedora-ws-centosci https://ci.centos.org/artifacts/sig-atomic/rdgo/fedora-workstation/ostree/repo/
+```
+
+Pull down the content (you can interrupt and restart this):
+```
+ostree --repo=/ostree/repo pull fedora-ws-centosci:fedora/24/x86_64/desktop/continuous
+```
+
+Initialize an "os" for this, which acts as a state root.
+```
+ostree admin os-init fedora
+```
+
+**For EFI systems**: currently ostree uses the presence of /boot/grub2/grub.cfg to detect a BIOS system,
+but that can be present on systems booted with EFI as well. If you boot with EFI
+(/sys/firmware/efi exists), then you need to move /boot/grub2/grub.cfg aside:
+```
+mv /boot/grub2/grub.cfg /boot/grub2/grub.cfg.bak
+```
+Since this file is not used on a EFI system, this won't break the operation of your current system. While you are at it, back up your existing grub config:
+```
+cp /boot/efi/EFI/fedora/grub.cfg /boot/efi/EFI/fedora/grub.cfg.bak
+```
+
+Deploy; we use `enforcing=0` to avoid SELinux issues for now.
+```
+ostree admin deploy --os=fedora --karg-proc-cmdline --karg=enforcing=0 fedora-ws-centosci:fedora/24/x86_64/desktop/continuous
+```
+
+To initialize this root, you'll need to copy over your `/etc/fstab`, `/etc/default/grub` at least, along with the ostree remote that we added:
+```
+for i in /etc/fstab /etc/default/grub /etc/ostree/remotes.d/fedora-ws-centosci.conf ; do cp $i /ostree/deploy/fedora/deploy/$checksum.0/$i; done
+```
+If you have a separate `/home` mount point, you'll need to change
+that `fstab` copy to refer to `/var/home`.
+
+You'll also need to copy your user entry from `/etc/passwd`, `/etc/group`,
+and `/etc/shadow` into the new `/etc/`, and add yourself to the wheel group
+in `/etc/group`. Don't copy just copy these files literally, however, since
+the system users and groups won't be the same.
+
+**For BIOS systems**: while ostree regenerated the bootloader configuration,
+it writes config into `/boot/loader/grub.cfg`.  On a current `grubby`
+system, you'll need to copy that version over:
+
+```
+cp /boot/loader/grub.cfg /boot/grub2/grub.cfg
+```
+
 Migrating between OSTree repos
 -------------------------------------