doc: ReSTify keys.txt

This creates a new section in the security development index for kernel
keys, and adjusts for ReST markup.

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

Author: kees

Documentation/crypto/asymmetric-keys.txt

@@ -265,7 +265,7 @@ mandatory:
 
      The caller passes a pointer to the following struct with all of the fields
      cleared, except for data, datalen and quotalen [see
-     Documentation/security/keys.txt].
+     Documentation/security/keys/core.rst].
 
 	struct key_preparsed_payload {
 		char		*description;

Documentation/security/00-INDEX

@@ -6,5 +6,3 @@ keys-request-key.txt
 	- description of the kernel key request service.
 keys-trusted-encrypted.txt
 	- info on the Trusted and Encrypted keys in the kernel key ring service.
-keys.txt
-	- description of the kernel key retention service.

Documentation/security/index.rst

@@ -7,6 +7,7 @@ Security Documentation
 
    credentials
    IMA-templates
+   keys/index
    LSM
    self-protection
    tpm/index