Add FAQ section to reasoning

Usage/Prompts/reasoning.md

@@ -10,6 +10,10 @@ This information refers to a pre-release feature that is still in development. I
 
 In language models, reasoning (also known as model thinking) refers to a chain-of-thought (CoT) technique that mirrors human problem-solving through step-by-step analysis. SillyTavern provides several features that make the use of reasoning models more efficient and consistent across supported backends.
 
+## Common issues
+
+1. When using reasoning models, the model's internal reasoning process consumes part of your response token allowance, even if this reasoning isn't shown in the final output (e.g. o3-mini or Gemini Thinking). If you notice your responses are coming back incomplete or empty, you should try adjusting the Max Response Length setting found in the **<i class="fa-solid fa-sliders"></i> AI Response Configuration** panel. For reasoning models, it's typical to use significantly higher token limits - anywhere from 1024 to 4096 tokens - compared to standard conversational models.
+
 ## Configuration
 
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