Replace HTTP links with HTTPS ones: Documentation/admin-guide

Rationale:
Reduces attack surface on kernel devs opening the links for MITM
as HTTPS traffic is much harder to manipulate.

Deterministic algorithm:
For each file:
  If not .svg:
    For each line:
      If doesn't contain `\bxmlns\b`:
        For each link, `\bhttp://[^# \t\r\n]*(?:\w|/)`:
          If both the HTTP and HTTPS versions
          return 200 OK and serve the same content:
            Replace HTTP with HTTPS.

Signed-off-by: Alexander A. Klimov <grandmaster@al2klimov.de>
Link: https://lore.kernel.org/r/20200627072935.62652-1-grandmaster@al2klimov.de
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/nfs/nfsroot.rst

@@ -264,7 +264,7 @@ They depend on various facilities being available:
      	access to the floppy drive device, /dev/fd0
 
      	For more information on syslinux, including how to create bootdisks
-     	for prebuilt kernels, see http://syslinux.zytor.com/
+     	for prebuilt kernels, see https://syslinux.zytor.com/
 
 	.. note::
 		Previously it was possible to write a kernel directly to
@@ -292,7 +292,7 @@ They depend on various facilities being available:
 	  cdrecord dev=ATAPI:1,0,0 arch/x86/boot/image.iso
 
      	For more information on isolinux, including how to create bootdisks
-     	for prebuilt kernels, see http://syslinux.zytor.com/
+     	for prebuilt kernels, see https://syslinux.zytor.com/
 
 - Using LILO
 
@@ -346,7 +346,7 @@ They depend on various facilities being available:
 	see Documentation/admin-guide/serial-console.rst for more information.
 
 	For more information on isolinux, including how to create bootdisks
-	for prebuilt kernels, see http://syslinux.zytor.com/
+	for prebuilt kernels, see https://syslinux.zytor.com/