Add top-level directory check for security.txt

security.txt files can be placed under the top-level directory too.
This commit adds a check for:

    https://example.com/security.txt

files/security.txt.yaml

@@ -9,6 +9,7 @@ requests:
   - method: GET
     path:
       - "{{BaseURL}}/.well-known/security.txt"
+      - "{{BaseURL}}/security.txt"
     matchers:
       - type: status
         status: