Add build instructions

README.md

@@ -6,6 +6,18 @@ Technical information about all Tornado Cash contracts, token distribution and E
 
 Node 12 or higher. This package doesn't have any other build dependencies.
 
+Install development dependencies:
+
+```bash
+npm i
+```
+
+### Build
+
+```bash
+npm run build
+```
+
 ### Licence
 
 MIT