docs: fix locations of several documents that got moved

The previous patch renamed several files that are cross-referenced
along the Kernel documentation. Adjust the links to point to
the right places.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
diff --git a/init/Kconfig b/init/Kconfig
index 34407f1..172f80e 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1306,7 +1306,7 @@
 	  boot loader (loadlin or lilo) and that is mounted as root
 	  before the normal boot procedure. It is typically used to
 	  load modules needed to mount the "real" root file system,
-	  etc. See <file:Documentation/initrd.txt> for details.
+	  etc. See <file:Documentation/admin-guide/initrd.rst> for details.
 
 	  If RAM disk support (BLK_DEV_RAM) is also included, this
 	  also enables initial RAM disk (initrd) support and adds