docs: Bump the version number in the install docs

Signed-off-by: andypugh <andy@bodgesoc.org>

Author: andypugh

docs/src/getting-started/getting-linuxcnc.txt

@@ -39,12 +39,12 @@ Image.
 
 For x86 PCs Download the Live/Install CD by clicking here:
 
-http://www.linuxcnc.org/iso/linuxcnc-2.8.2-buster.iso
+http://www.linuxcnc.org/iso/linuxcnc-2.8.4-buster.iso
 
 For the Raspberry Pi a complete SD card image is available here:
 
 http://www.linuxcnc.org/iso/linuxcnc-2.8.1-pi4.zip (this will auto-update
-to 2.8.2 )
+to 2.8.4 )
 
 This can be installed using the normal Pi
 https://www.raspberrypi.org/documentation/installation/installing-images/README.md[install process]
@@ -77,7 +77,7 @@ sudo apt-get install zsync
 . Then run this command to download the iso to your computer
 +
 ----
-http://www.linuxcnc.org/iso/linuxcnc-2.8.2-buster.iso
+zsync http://www.linuxcnc.org/iso/linuxcnc-2.8.4-buster.iso
 ----
 +
 or
@@ -100,13 +100,13 @@ https://www.assembla.com/spaces/zsync-windows/documents
 . After downloading, verify the checksum of the image to ensure integrity.
 +
 ----
-md5sum linuxcnc-2.8.2-buster.iso
+md5sum linuxcnc-2.8.4-buster.iso
 ----
 +
 or
 +
 ----
-sha256sum linuxcnc-2.8.2-buster.iso
+sha256sum linuxcnc-2.8.4-buster.iso
 ----
 . Then compare to these checksums
 +
@@ -143,7 +143,7 @@ used to boot a computer.  The image is too large to fit on a CD.
   then use this command:
 +
 -----
-dd if=linuxcnc-2.8.2-buster.iso of=/dev/sde
+dd if=linuxcnc-2.8.4-buster.iso of=/dev/sde
 -----
 
 .Writing the image to a USB storage device in Mac OSX
@@ -336,7 +336,8 @@ sudo apt-get install linux-image-rt-amd64
 
 ----
 
-. Re-boot, and select the Linux 4.19.0-9-rt-amd64 kernel. This might be
+. Re-boot, and select the Linux 4.19.0-9-rt-amd64 kernel (the exact
+kernel version might be different, look for the "-rt" suffix. This might be
 hidden in the "Advanced options for Debian Buster" sub-menu in Grub.
 When you
   log in, verify that `PREEMPT RT`is reported by the following command.