docs(graphql): add query complexity limit (#130)

docs/graphql/intro/ratelimiting/index.md

@@ -12,7 +12,7 @@ Here we will provide an overview of managing request quotas.
 
 ## Response Headers
 
-The AnimeThemes GraphQL API limits queries to 90 per minute.
+The AnimeThemes GraphQL API limits 90 requests per minute.
 
 The AnimeThemes API will return `X-RateLimit-Limit` and `X-RateLimit-Remaining` headers in the response.
 
@@ -25,7 +25,7 @@ X-RateLimit-Remaining: 89
 
 ## Exceeding the Rate Limit
 
-If the rate limit is exceeded, the AnimeThemes API will return `Retry-After` and `X-RateLimit-Reset` headers in the response.
+If the rate limit is exceeded, the AnimeThemes API will return `Retry-After` and `X-RateLimit-Reset` headers in the response with a 429 status code.
 
 ```sh
 ...
@@ -50,7 +50,7 @@ Clients can nest fields within other fields, which can quickly result in deeply
 
 The AnimeThemes GraphQL API enforces a maximum query depth of 13.
 
-If your query exceeds this limit, the API will return the following error response:
+If your query exceeds this limit, the API will return a 200 status code with the following error response:
 
 ```json
 {
@@ -60,4 +60,22 @@ If your query exceeds this limit, the API will return the following error respon
         }
     ]
 }
+```
+
+## Query Complexity Limit
+
+Clients can request a lot of fields, can nest fields within other fields, which can quickly result in deeply nested queries.
+
+The AnimeThemes GraphQL API enforces a maximum of 250 fields per request.
+
+If your query exceeds this limit, the API will return a 200 status code with the following error response:
+
+```json
+{
+    "errors": [
+        {
+            "message": "Max query complexity should be 250 but got 300."
+        }
+    ]
+}
 ```