add npm install and npm run build instructions to READMEs

Signed-off-by: danbugs <danilochiarlone@gmail.com>

Author: danbugs

README.md

@@ -23,6 +23,7 @@ cargo run -- guest-examples/hello.py
 Run from JavaScript/Node.js:
 
 ```bash
+npm install
 npm run build
 node examples/napi.js
 ```

examples/ai-generated-scripts/README.md

@@ -7,6 +7,8 @@ AI-generated code from LLMs is untrusted and should never run directly in the ho
 1. Pack the hyperlight-nanvix package from the root:
 ```bash
 cd ../..
+npm install
+npm run build
 npm pack
 ```