doc: ReSTify credentials.txt

This updates the credentials API documentation to ReST markup and moves
it under the security subsection of kernel API documentation.

Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/security/00-INDEX

@@ -10,8 +10,6 @@ Yama.txt
 	- documentation on the Yama Linux Security Module.
 apparmor.txt
 	- documentation on the AppArmor security extension.
-credentials.txt
-	- documentation about credentials in Linux.
 keys-ecryptfs.txt
 	- description of the encryption keys for the ecryptfs filesystem.
 keys-request-key.txt

Documentation/security/index.rst

@@ -5,5 +5,6 @@ Security Documentation
 .. toctree::
    :maxdepth: 1
 
+   credentials
    IMA-templates
    tpm/index

include/linux/cred.h

-/* Credentials management - see Documentation/security/credentials.txt
+/* Credentials management - see Documentation/security/credentials.rst
  *
  * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
  * Written by David Howells (dhowells@redhat.com)

kernel/cred.c

-/* Task credentials management - see Documentation/security/credentials.txt
+/* Task credentials management - see Documentation/security/credentials.rst
  *
  * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
  * Written by David Howells (dhowells@redhat.com)