doc: fix gsg instructions for building the acrn-kernel

You need to be in the acrn-kernel directory in order to ``run make
distclean`` Also remove mention of 6 vms...

Signed-off-by: David B. Kinder <[email protected]>

Author: dbkinder

doc/getting-started/getting-started.rst

@@ -567,6 +567,7 @@ Build ACRN
 
       .. code-block:: bash
 
+         cd ~/acrn-work/acrn-kernel
          make distclean
 
    #. Build the ACRN kernel:
@@ -606,9 +607,6 @@ Build ACRN
          cp ~/acrn-work/acpica-unix-20210105/generate/unix/bin/iasl "$disk"/
          sync && sudo umount "$disk"
 
-      Even though our sample default scenario defines six User VMs, we're only
-      going to launch one of them, so we'll only need the one launch script.
-
    #. Insert the USB disk you just used into the target system and run these
       commands to copy the files locally: