Add claraifications to the kproc and kthread manpages and link

the kthread_create(9) man page to the kproc(9) page as it had migrated and
people looking for it may need a hand to find its new name.

MFC after:	1 week

share/man/man9/Makefile

@@ -713,6 +713,7 @@ MLINKS+=kobj.9 DEFINE_CLASS.9 \
 	kobj.9 kobj_delete.9 \
 	kobj.9 kobj_init.9
 MLINKS+=kproc.9 kproc_create.9 \
+	kproc.9 kthread_create.9 \
 	kproc.9 kproc_exit.9 \
 	kproc.9 kproc_resume.9 \
 	kproc.9 kproc_shutdown.9 \

share/man/man9/kproc.9

@@ -64,6 +64,28 @@
 .Fa "int flags" "int pages" "char * procname" "const char *fmt" "..."
 .Fc
 .Sh DESCRIPTION
+In
+.Fx 8.0 ,
+the
+.Fn kthread* 9
+family of functions was renamed to be the
+.Fn kproc* 9
+family of functions, as they were misnamed
+and actually produced kernel processes.
+A new family of
+.Em different
+.Fn kthread_* 9
+functions was added to produce
+.Em real
+kernel 
+.Em threads . 
+See the
+.Xr kthread 9
+man page for more information on those calls.
+Also note that the
+.Fn kproc_kthread_add 9
+function appears in both pages as its functionality is split.
+.Pp
 The function
 .Fn kproc_start
 is used to start

share/man/man9/kthread.9

@@ -65,6 +65,27 @@
 .Fa "int flags" "int pages" "char * procname" "const char *fmt" "..."
 .Fc
 .Sh DESCRIPTION
+In
+.Fx 8.0 ,
+the older family of
+.Fn kthread_* 9
+functions was renamed to be the
+.Fn  kproc_* 9
+family of functions,
+as they were previously misnamed
+and actually produced kernel processes.
+This new family of
+.Fn kthread_* 9
+functions was added to produce
+.Em real
+kernel threads.
+See the
+.Xr kproc 9
+man page for more information on the renamed calls.
+Also note that the 
+.Fn kproc_kthread_add 9
+function appears in both pages as its functionality is split.
+.Pp
 The function
 .Fn kthread_start
 is used to start