docs: describe caching optimization statistics feature in README

Author: mu-hun

README.md

@@ -262,6 +262,33 @@ The logger supports the following log levels:
 
 The logger is initialized during compilation when a valid `logPath` is provided.
 
+## Local Optimization Config
+
+`localOptimizationConfig` provides a workflow for caching optimization statistics
+locally so that `compile()` reads them from disk instead of fetching from the remote server.
+
+### Directory layout
+
+```text
+<configPath>/
+  percent.json                   # lists which filters have stats (PERCENT_JSON)
+  filters/
+    <filterId>/
+      stats.json                 # per-filter hit counts (STATS_JSON)
+```
+
+### Workflow
+
+1. Call `downloadPercentJson(configPath)` to download `percent.json` from the
+   remote server and save it to `configPath`.
+2. Call `downloadStatsFromPercentJson(configPath, filterIds)` to download
+   per-filter `stats.json` files listed in `percent.json`. An empty `filterIds`
+   processes all filters; a non-empty array limits processing to specific filter IDs.
+3. Call `useLocalConfig(configPath)` before `compile()` to tell the compiler to
+   read optimization stats from disk instead of the remote server.
+4. Call `reset(configPath)` when done to remove the cache directory and clear
+   in-memory state.
+
 ## Additional resources
 
 - [AGENTS.md](AGENTS.md) — AI agent instructions and code guidelines