docs: fix formatting in MANUAL_STEPS.md (#2484)

Author: richardlau

ansible/MANUAL_STEPS.md

@@ -462,7 +462,7 @@ pxe-service=0,"Raspberry Pi Boot"
 * Copy the entirety of the boot partition of the Raspbian disk image into a subdirectory for each Pi. Symlinks are acceptable to map serial numbers to the names of the Pi's to keep them organised properly.
 * Edit cmdline.txt inside the tftp subdirectory for each file and replace the contents with:
 
-``
+```
 modprobe.blacklist=bcm2835_v4l2 root=/dev/nfs nfsroot=NFS_ROOT_SERVER_IP:/NFS_ROOT_FOR_THIS_PI,vers=3 rw ip=dhcp rootwait elevator=deadline
 ```
 
@@ -478,8 +478,6 @@ An NFS root server can be separate from NFS boot server, and could be different
 * The ext4 partition of the Raspbian image file (second partition, not the boot FAT partition) should be extracted into this root directory.
 * `etc/fstab` in the root directory should be edited to make it NFS compatible. Remove the existing `/boot` and `/` entries and replace them with:
 
-```
-
 ```
 /dev/mmcblk0p1 /mnt/mmcblk0p1 vfat defaults 0 0
 NFS_ROOT_SERVER_IP:PATH_TO_SHARED_CCACHE_DIRECTORY /home/iojs/.ccache nfs4 rw,exec,async,noauto 0 0