CDN rate limit clarification (#919)

* Update cdn_purge_cache.yml

Updates CDN cache purge description.

* Update DigitalOcean-public.v2.yaml

Updates main description for CDN endpoints with request limit.

specification/DigitalOcean-public.v2.yaml

@@ -112,7 +112,9 @@ tags:
       create, or delete CDN Endpoints as well as purge cached content. To use a
       custom subdomain to access the CDN Endpoint, provide the ID of a
       DigitalOcean managed TLS certificate and the fully qualified domain name
-      for the custom subdomain.
+      for the custom subdomain. 
+
+      CDN endpoints have a rate limit of five requests per 10 seconds.
 
   - name: Certificates
     description: |-

specification/resources/cdn/cdn_purge_cache.yml

@@ -7,9 +7,11 @@ description: |
   `/v2/cdn/endpoints/$ENDPOINT_ID/cache`. The body of the request should include
   a `files` attribute containing a list of cached file paths to be purged. A
   path may be for a single file or may contain a wildcard (`*`) to recursively
-  purge all files under a directory. When only a wildcard is provided, all
-  cached files will be purged. There is a rate limit of 50 files per 20 seconds 
-  that can be purged.
+  purge all files under a directory. When only a wildcard is provided, all cached 
+  files will be purged. There is a rate limit of 50 files per 20 seconds that can 
+  be purged. CDN endpoints have a rate limit of 5 requests per 10 seconds. 
+  Purging files using a wildcard path counts as a single request against the API's 
+  rate limit. Two identical purge requests cannot be sent at the same time.
 
 tags:
   - CDN Endpoints