Document assistant API limits (#914)

* update intro

* add limits

* remove example using old API

* reviewer feedback

Author: ethanpalm

api-reference/chat/create-assistant-message.mdx

@@ -1,3 +1,11 @@
 ---
 openapi: POST /assistant/{domain}/message
 ---
+
+## Rate limits
+
+The assistant API has the following limits:
+
+- 10,000 uses per key per month
+- 10,000 requests per Mintlify organization per hour
+- 10,000 requests per IP per day

api-reference/introduction.mdx

@@ -3,18 +3,12 @@ title: Introduction
 icon: "book-open"
 ---
 
-## Trigger Updates
-
-You can leverage the REST API to programmatically trigger an update when desired.
-
 ## Authentication
 
-You can generate an API key through
-[the dashboard](https://dashboard.mintlify.com/settings/organization/api-keys). The API key is
-associated with the entire org and can be used across multiple deployments.
+You can generate an API key through [the dashboard](https://dashboard.mintlify.com/settings/organization/api-keys). The API key is associated with an entire organization and can be used across multiple deployments.
 
 <Frame>
-  <img src="/images/external-api-key.png" />
+  <img alt="Screenshot of the API keys page in the Mintlify dashboard." src="/images/external-api-key.png" />
 </Frame>
 
 ## Admin API key
@@ -23,15 +17,12 @@ The Admin API key is used for the majority of the API. It is used to trigger upd
 
 ## Assistant API key
 
-The Assistant API allows you to embed the AI assistant experience grounded in your docs and continually kept up to date into any application of your choosing.
+The assistant API allows you to embed the AI assistant, trained on your docs and continually kept up to date, into any application of your choosing.
 
-Responses include citations so you can point your users to the right places they need to get help.
+Responses include citations so you can point your users to the right destinations for more information.
 
 <Note>
-  The Assistant API token is a public token that can be referenced in your
-  frontend code whereas the API key is a server-side token that should be kept
-  secret.
+  The assistant API **token** is a public token that can be referenced in your frontend code. The API **key** is a server-side token that should be kept secret.
+  
+  Calls using the assistant API token can incur costs: either using your AI chat credits or incurring overages.
 </Note>
-
-Now that you have an API key, check out our [example](https://github.com/mintlify/discovery-api-example) for how to use
-the API for AI assistant. You can also see a deployed version of this example at [chat.mintlify.com](https://chat.mintlify.com).