README.org: Minor additions and new section about substitutes

* README.org:
(Disk Setup and Partitioning): Document creating and enabling swap and creating/mounting /boot/efi
(Optional (but recommended): Use additional or alternative substitute servers): New section

README.org

@@ -166,10 +166,20 @@ TODO: disks need to be partitioned and appropriately mounted. This varies depend
   btrfs subvolume create /mnt/gnu/store
   btrfs subvolume create /mnt/home
   btrfs subvolume create /mnt/var
+
+  # Create and activate swap
+  mkswap --label swap /dev/vg0/swap
+  swapon /dev/vg0/swap
+
+  # Prepare /mnt for Guix installation
+  mkdir -p /mnt/boot/efi
+  mount /dev/nvme0n1p1 /mnt/boot/efi
 #+end_src
 
 *** Bootstrap System
 
+**** Start ~cow-store~ Service
+
 As described in guix documentation, start ~cow-store~ to allow later steps to write store
 changes to ~/mnt/gnu/store~.
 
@@ -177,16 +187,29 @@ changes to ~/mnt/gnu/store~.
   herd start cow-store /mnt
 #+end_src
 
-Create a ~bootstrap.scm~ file like this:
+**** Optional (but recommended): Use additional or alternative substitute servers
 
-#+begin_src scheme
-  (@ (rekahsoft guix-config <vms|manual> <target>) %system)
-#+end_src
+Optionally additional or alternative substitute servers can be setup for guix-daemon. This is
+recommended to greatly speed up installation (so that nonguix and rekahsoft-guix (internal
+network only) substitutes can be used).
 
-Use ~guix system init ...~ to instantiate the system.
+First stop the running ~guix-daemon~.
 
 #+begin_src bash
-  guix system init bootstrap.scm /mnt
+  herd stop guix-daemon
+#+end_src
+
+Then start a new instance of ~guix-daemon~ as it is normally started by its Shepherd service,
+but with additional or alternative substitute servers provided.
+
+#+begin_src bash
+  guix-daemon \
+    --build-users-group guixbuild \
+    --max-silent-time 0 \
+    --timeout 0 \
+    --log-compression gzip \
+    --discover=no \
+    --substitute-urls https://substitutes.nonguix.org https://guix-ci.home.rekahsoft.ca https://ci.guix.gnu.org https://bordeaux.guix.gnu.org &
 #+end_src
 
 **** Create and Bootstrap System