docs(personalization): add rate limit information for personalization API

Author: Keylor42

specs/personalization/spec.yml

@@ -37,6 +37,18 @@ info:
     Successful responses return a `2xx` status. Client errors return a `4xx` status. Server errors are indicated by a `5xx` status.
     Error responses have a `message` property with more information.
 
+    ## Rate limiting
+
+    When making requests to the Personalization API, you are limited to 40 API calls per second per application.
+
+    The following headers provide information about your current limit:
+
+    - `x-ratelimit-limit`: The number of requests allowed every second.
+    - `x-ratelimit-remaining`: The number of requests remaining in the current
+    second period.
+    - `x-ratelimit-reset`: [Unix timestamp](https://www.unixtimestamp.com/) of
+    the next time period.
+
     ## Version
 
     The current version of the Personalization API is version 1, as indicated by the `/1/` in each endpoint's URL.