minor #3700 [Cookbook][Security] Firewall restrictions tweaks (xabbuh)

This PR was merged into the master branch.

Discussion
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[Cookbook][Security] Firewall restrictions tweaks

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.5+
| Fixed tickets |

Commits
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70b55b5 fix literal
ddf5fe4 add firewall restriction document to security toctree

Author: weaverryan

cookbook/security/firewall_restriction.rst

@@ -65,7 +65,7 @@ matches the configured ``pattern``.
         ));
 
 The ``pattern`` is a regular expression. In this example, the firewall will only be 
-activated if the URL starts (due to the ``^`` regex character) with ``/admin`. If 
+activated if the URL starts (due to the ``^`` regex character) with ``/admin``. If 
 the URL does not match this pattern, the firewall will not be activated and subsequent 
 firewalls will have the opportunity to be matched for this request.
 

cookbook/security/index.rst

@@ -13,6 +13,7 @@ Security
     acl_advanced
     force_https
     host_restriction
+    firewall_restriction
     form_login
     securing_services
     custom_provider