Documentation: Update kernel-parameters.tx

1) __setup() is messy, prefer module_param and core_param.
2) Document --
3) Document modprobe scraping /proc/cmdline.
4) Document handing of leftover parameters to init.
5) Document use of quotes to protect whitespace.
Reported-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Documentation/kernel-parameters.txt

                           Kernel Parameters
                           ~~~~~~~~~~~~~~~~~
 
-The following is a consolidated list of the kernel parameters as implemented
-(mostly) by the __setup() macro 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.
-
-Module parameters for loadable modules are specified only as the
-parameter name with optional '=' and value as appropriate, such as:
-
-	modprobe usbcore blinkenlights=1
-
-Module parameters for modules that are built into the kernel image
-are specified on the kernel command line with the module name plus
-'.' plus parameter name, with '=' and value if appropriate, such as:
-
-	usbcore.blinkenlights=1
+The following is a consolidated list of the kernel parameters as
+implemented by the __setup(), 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.
+
+The kernel parses parameters from the kernel command line up to "--";
+if it doesn't recognize a parameter and it doesn't contain a '.', the
+parameter gets passed to init: parameters with '=' go into init's
+environment, others are passed as command line arguments to init.
+Everything after "--" is passed as an argument to init.
+
+Module parameters can be specified in two ways: via the kernel command
+line with a module name prefix, or via modprobe, e.g.:
+
+	(kernel command line) usbcore.blinkenlights=1
+	(modprobe command line) modprobe usbcore blinkenlights=1
+
+Parameters for modules which are built into the kernel need to be
+specified on the kernel command line.  modprobe looks through the
+kernel command line (/proc/cmdline) and collects module parameters
+when it loads a module, so the kernel command line can be used for
+loadable modules too.
 
 Hyphens (dashes) and underscores are equivalent in parameter names, so
 	log_buf_len=1M print-fatal-signals=1
 can also be entered as
 	log-buf-len=1M print_fatal_signals=1
 
+Double-quotes can be used to protect spaces in values, e.g.:
+	param="spaces in here"
 
 This document may not be entirely up to date and comprehensive. The command
 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable