Documentation: fix typo for core-api/cpu_hotplug documentation

fix typo for core-api/cpu_hotplug documentation
Signed-off-by: Yaohui Wang <dillionmango@gmail.com>
Link: https://lore.kernel.org/r/20200722073818.20605-1-dillionmango@gmail.comSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/core-api/cpu_hotplug.rst

@@ -35,8 +35,8 @@ Command Line Switches
   other CPUs later online.
 
 ``nr_cpus=n``
-  Restrict the total amount CPUs the kernel will support. If the number
-  supplied here is lower than the number of physically available CPUs than
+  Restrict the total amount of CPUs the kernel will support. If the number
+  supplied here is lower than the number of physically available CPUs, then
   those CPUs can not be brought online later.
 
 ``additional_cpus=n``