docs: Added requirements and updated screenshot. (#6)

README.md

@@ -7,6 +7,15 @@ Application Firewall.
 
 ![Screenshot of the Datadog WAF Dashboard][screenshot-dashboard]
 
+## Requirements
+
+This dashboard assumes that your logs are tagged with `source:waf` and
+`webacl:*`, where `webacl` is the name of the WebACL that the log is associated
+with. There are multiple ways to accomplish this, but the easiest is to tag the
+CloudWatch log group with the appropriate tags, and ensure that
+`DdFetchLogGroupTags` is set to `true` in the [log forwarder
+stack][aws-forwarder].
+
 ## Usage
 
 Add this module to your `main.tf` (or appropriate) file and configure the inputs
@@ -48,8 +57,9 @@ tofu init -upgrade
 | threshold_limited_warning | Warning threshold for rate limited requests. Reflected when the percentage of rate limited requests rises above this number. | `number`       | `10`                               | no       |
 | title                     | Title of the dashboard.                                                                                                      | `string`       | `"Web Application Firewall (WAF)"` | no       |
 
+[aws-forwarder]: https://docs.datadoghq.com/logs/guide/forwarder/?tab=cloudformation#advanced-optional
 [badge-checks]: https://github.com/codeforamerica/tofu-modules-datadog-waf-dashboard/actions/workflows/main.yaml/badge.svg
 [badge-release]: https://img.shields.io/github/v/release/codeforamerica/tofu-modules-datadog-waf-dashboard?logo=github&label=Latest%20Release
 [code-checks]: https://github.com/codeforamerica/tofu-modules-datadog-waf-dashboard/actions/workflows/main.yaml
 [latest-release]: https://github.com/codeforamerica/tofu-modules-datadog-waf-dashboard/releases/latest
-[screenshot-dashboard]: docs/assets/dashboard.jpeg
+[screenshot-dashboard]: docs/assets/dashboard.png