build: add local setup README pointer

Author: stacknil

README.md

@@ -80,15 +80,17 @@ LogLens does not currently detect:
 - PAM-specific failures beyond the parsed sample patterns
 - Cross-file or cross-host correlation
 
-## Build
-
-```bash
-cmake -S . -B build
-cmake --build build
-ctest --test-dir build --output-on-failure
-```
-
-## Run
+## Build
+
+```bash
+cmake -S . -B build
+cmake --build build
+ctest --test-dir build --output-on-failure
+```
+
+For fresh-machine setup and repeatable local presets, see [`docs/dev-setup.md`](./docs/dev-setup.md).
+
+## Run
 
 ```bash
 ./build/loglens --mode syslog --year 2026 ./assets/sample_auth.log ./out