Documentation: admin: early_param()s are also listed in kernel-parameters

Add info that "early_param()" kernel boot parameters are also listed
in kernel-parameters.txt.
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Link: https://lore.kernel.org/r/20201226174433.7885-1-rdunlap@infradead.orgSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/kernel-parameters.rst

@@ -3,8 +3,8 @@
 The kernel's command-line parameters
 ====================================
 
-The following is a consolidated list of the kernel parameters as
-implemented by the __setup(), core_param() and module_param() macros
+The following is a consolidated list of the kernel parameters as implemented
+by the __setup(), early_param(), core_param() and module_param() macros
 and sorted into English Dictionary order (defined as ignoring all
 punctuation and sorting digits before letters in a case insensitive
 manner), and with descriptions where known.