chore: add field-policies to README (#99)

Author: CodeShellDev

.github/templates/README.template.md

@@ -54,6 +54,7 @@ Check out the official [Documentation](https://codeshelldev.github.io/secured-si
 - [Configuration](#configuration)
   - [Endpoints](#endpoints)
   - [Variables](#variables)
+  - [Field Policies](#field-policies)
   - [Field Mappings](#field-mappings)
   - [Message Templates](#message-templates)
 - [Integrations](https://codeshelldev.github.io/secured-signal-api/docs/integrations/compatibility)
@@ -284,6 +285,23 @@ settings:
 Message Templates support [Standard Golang Templating](#templating).
 Use `@data.key` to reference Body Keys, `#Content_Type` for Headers and `.KEY` for Variables.
 
+### Field Policies
+
+**Field Policies** allow for blocking or specifically allowing certain fields with set values from being used in the requests body or headers.
+
+Configure them by using `access.fieldPolicies` like so:
+
+```yaml
+settings:
+  access:
+    fieldPolicies:
+      "@number": { value: "+123400002", action: block }
+```
+
+Set the wanted action on encounter, available options are `block` and `allow`.
+
+Use `@` for Body Keys and `#` for Headers.
+
 ### Field Mappings
 
 To improve compatibility with other services Secured Signal API provides **Field Mappings** and a built-in `message` Mapping.