docs: add reading-the-dashboard guide to README

Lists common signals in the dashboard (cache hit, retry rate,
model mix, tool patterns) and what each typically means.
Points readers toward interpreting their own data without
overpromising automatic diagnosis.

README.md

@@ -149,6 +149,23 @@ Requires [SwiftBar](https://github.com/swiftbar/SwiftBar) (`brew install --cask
 
 **Pricing**: Fetched from [LiteLLM](https://github.com/BerriAI/litellm) model prices (auto-cached 24h at `~/.cache/codeburn/`). Handles input, output, cache write, cache read, and web search costs. Fast mode multiplier for Claude. Hardcoded fallbacks for all Claude and GPT-5 models to prevent fuzzy matching mispricing.
 
+## Reading the dashboard
+
+CodeBurn surfaces the data, you read the story. A few patterns worth knowing:
+
+| Signal you see | What it might mean |
+|---|---|
+| Cache hit < 80% | System prompt or context isn't stable, or caching not enabled |
+| Lots of `Read` calls per session | Agent re-reading same files, missing context |
+| Low 1-shot rate (Coding 30%) | Agent struggling with edits, retry loops |
+| Opus 4.6 dominating cost on small turns | Overpowered model for simple tasks |
+| `dispatch_agent` / `task` heavy | Sub-agent fan-out, expected or excessive |
+| No MCP usage shown | Either you don't use MCP servers, or your config is broken |
+| Bash dominated by `git status`, `ls` | Agent exploring instead of executing |
+| Conversation category dominant | Agent talking instead of doing |
+
+These are starting points, not verdicts. A 60% cache hit on a single experimental session is fine. A persistent 60% cache hit across weeks of work is a config issue.
+
 ## How it reads data
 
 **Claude Code** stores session transcripts as JSONL at `~/.claude/projects/<sanitized-path>/<session-id>.jsonl`. Each assistant entry contains model name, token usage (input, output, cache read, cache write), tool_use blocks, and timestamps.