Update Betterleaks config documentation

Author: dobri1408

.gitleaks.toml

@@ -1,4 +1,4 @@
-title = "volto-eea-website-theme Betterleaks config"
+title = "Betterleaks config"
 
 [extend]
 useDefault = true

README.md

@@ -119,6 +119,52 @@ See [RELEASE.md](https://github.com/eea/volto-eea-design-system/blob/master/RELE
 
 See [DEVELOP.md](https://github.com/eea/volto-eea-design-system/blob/master/DEVELOP.md).
 
+## Secret Scanning
+
+This repository uses the Betterleaks GitHub Action to scan the current
+repository content on every push and pull request. The scan uses the rules in
+`.gitleaks.toml` and uploads a `betterleaks-report` artifact when a finding is
+detected.
+
+There are three common outcomes:
+
+1. **Everything is OK.** The `Betterleaks / Scan for secrets` check is green and
+   no action is needed. Regular references to runtime values are OK, for example:
+
+   ```js
+   const tokenFromCookie = req.universalCookies.get('auth_token');
+   ```
+
+2. **A real secret was found.** The check is red and the workflow log asks you to
+   download the `betterleaks-report` artifact. Open the artifact from the GitHub
+   Actions run and check the reported file, line and rule. Remove the committed
+   value, move it to the proper secret store, and rotate it if it was exposed.
+   A report entry looks like this:
+
+   ```json
+   {
+     "RuleID": "secret-literal-assignment",
+     "File": "src/config.js",
+     "StartLine": 12,
+     "Secret": "[REDACTED]"
+   }
+   ```
+
+3. **The finding is a false positive.** Keep the value only if it is clearly not
+   sensitive, such as a test fixture, placeholder, or public example. Add
+   `betterleaks:allow` on the same line and include a short explanation in the
+   pull request.
+
+   ```js
+   const testPassword = 'admin'; //betterleaks:allow
+   ```
+
+   ```yaml
+   password: "admin" #betterleaks:allow
+   ```
+
+Do not add `betterleaks:allow` to real credentials.
+
 ## Copyright and license
 
 The Initial Owner of the Original Code is European Environment Agency (EEA).