diff --git a/README.md b/README.md
index 1a4f511..6528438 100644
--- a/README.md
+++ b/README.md
@@ -8,3 +8,10 @@ CDMA/GSM voice,sms and data is working now.
 
 * can't switch mobile data baseband correctly without restart networks.
 
+## How to build
+
+1. `extract-files.sh` to extract vendor files. Support pull from adb automatically or using path argument to extract.
+2. `setup-makefiles.sh` to generate vendor file makefiles.
+3. `lunch` & `brunch`
+
+Notice: source in `/overlay` may be **outdated**. The overlay contains modification of Captive Portal and `realcall` parameter setter when audio state is changing.
\ No newline at end of file