compiling instruction

Author: phiresky

README.md

@@ -170,3 +170,14 @@ And you should see the output to the query `select * from mytable`.
 ```
 
 The full code of this example is in [example/](./example/).
+
+## Compiling
+
+To compile this project (only needed if you want to modify the library itself), make sure you have emscripten, then first compile sql.js, then sql.js-httpvfs:
+
+```
+cd sql.js
+yarn build
+cd ..
+yarn build
+```