Add information for users providing their own keys.

src/gened/templates/instructor_class_config.html

@@ -147,6 +147,7 @@ <h2 class="title is-size-4 mt-5">Language Model</h2>
         <div class="field is-horizontal">
           <div class="field-label is-normal">
             <label class="label">OpenAI API Key:</label>
+            <p class="help-text">Your key must be in a <a href="https://platform.openai.com/docs/guides/rate-limits/usage-tiers">usage tier</a> that allows for the level of usage you expect.  The free tier does not support the models used here.</p>
             <p class="help-text">If blank, users in this class will not be able to submit queries.</p>
           </div>
           <div class="field-body">