ima: added ima-sig template among choices in kernel-parameters.txt

This patch adds the template 'ima-sig' among choices for the kernel
parameter 'ima_template'.
Signed-off-by: Roberto Sassu <rsassu@suse.de>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

Documentation/kernel-parameters.txt

@@ -1406,7 +1406,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 
 	ima_template=   [IMA]
 			Select one of defined IMA measurements template formats.
-			Formats: { "ima" | "ima-ng" }
+			Formats: { "ima" | "ima-ng" | "ima-sig" }
 			Default: "ima-ng"
 
 	ima_template_fmt=