Update README.md

Author: ineskhou

README.md

@@ -47,6 +47,12 @@ Finally, install the Zephyr SDK.
 west sdk install
 ```
 
+Finally, everytime you pull a new version of code, run this
+
+```
+git submodule update --init --recursive
+```
+
 ## Running the code
 
 Run generate from the `proves-core-reference` directory. This generates the build cache for FPrime. When you regenerate, append a -f, this will purge the previous deployment. You only need to do generate if something in the core FPrime package has changes