SECURITY: be consistent on the hash algorithm used

The SECURITY doc mentioned both SHA1 and SHA256.
Although this is configurable, the documentation should be
consistent on what the default actually is.
By looking at the `encrypt_and_sign` function it used
`instance->crypto_hash_type` which is set in `totem_get_crypto`,
defaulting to `sha1` if not overriden.

Signed-off-by: Török Edwin <edwintorok@users.noreply.github.com>
Reviewed-by: Jan Friesse <jfriesse@redhat.com>

SECURITY

@@ -53,10 +53,12 @@ encrypt_and_sign to prepare the message to be sent.  When the executive
 wants to receive a message from the network, it uses
 authenticate_and_decrypt to verify the message is valid and decrypt it.
 
-Corosync uses AES256/SHA-1 which from the Mozilla Network Security
+Corosync uses AES256/SHA-1 by default from the Mozilla Network Security
 Services (libnss) library.
+It supports the following choices for ciphers: 3des, aes128, aes192, aes256,
+and the following choices for hash algorithms: md5, sha1, sha256, sha384, sha512.
 
-The internal functions utilize the following algorithms:
+The internal functions utilize the following algorithms by default:
 sha1 - hash algorithm secure for using with hmac
 hmac - produces a 16 byte digest from any length input
 
@@ -73,8 +75,8 @@ the private key is read into memory and stored for later use by the code.
 
 When a message is sent (encrypt_and_sign):
 ------------------------------------------
-- The message is encrypted using AES.
-- A digest of that message is then created using SHA256 and based on the
+- The message is encrypted using the chosen cipher (AES256 by default).
+- A digest of that message is then created using the chosen hash algorithm (SHA1 by default) and based on the
   private key.
 - the message is then transmitted.