Clarify unanimous access strategy description

Steveb-p · javiereguiluz · commit 94d6f30cffdc · 2018-03-01T15:20:36.000+01:00
diff --git a/security/voters.rst b/security/voters.rst
@@ -251,7 +251,9 @@ strategies available:
     This grants access if there are more voters granting access than denying;
 
 ``unanimous``
-    This only grants access once *all* voters grant access.
+    This only grants access if there is no voter denying access. 
+    ``allow_if_all_abstain`` configuration option can be used if voter granting 
+    access is also required.
 
 In the above scenario, both voters should grant access in order to grant access
 to the user to read the post. In this case, the default strategy is no longer
