update readme to include reporting info

Author: KyFaSt

README.md

@@ -88,9 +88,50 @@ SecureHeaders::Configuration.default do |config|
     img_src: %w(somewhereelse.com),
     report_uri: %w(https://report-uri.io/example-csp-report-only)
   })
+
+  # Optional: Use the modern report-to directive (with Reporting-Endpoints header)
+  config.csp = config.csp.merge({
+    report_to: "csp-endpoint"
+  })
+
+  # When using report-to, configure the reporting endpoints header
+  config.reporting_endpoints = {
+    "csp-endpoint": "https://report-uri.io/example-csp",
+    "csp-report-only": "https://report-uri.io/example-csp-report-only"
+  }
 end
 ```
 
+### CSP Reporting
+
+SecureHeaders supports both the legacy `report-uri` and the modern `report-to` directives for CSP violation reporting:
+
+#### report-uri (Legacy)
+The `report-uri` directive sends violations to a URL endpoint. It's widely supported but limited to POST requests with JSON payloads.
+
+```ruby
+config.csp = {
+  default_src: %w('self'),
+  report_uri: %w(https://example.com/csp-report)
+}
+```
+
+#### report-to (Modern)
+The `report-to` directive specifies a named reporting endpoint defined in the `Reporting-Endpoints` header. This enables more flexible reporting through the HTTP Reporting API standard.
+
+```ruby
+config.csp = {
+  default_src: %w('self'),
+  report_to: "csp-endpoint"
+}
+
+config.reporting_endpoints = {
+  "csp-endpoint": "https://example.com/reports"
+}
+```
+
+**Recommendation:** Use both `report-uri` and `report-to` for maximum compatibility while transitioning to the modern approach.
+
 ### Deprecated Configuration Values
 * `block_all_mixed_content` - this value is deprecated in favor of `upgrade_insecure_requests`. See https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/block-all-mixed-content for more information.