Update build_custom_prompter.sh

build_custom_prompter.sh

@@ -1,4 +1,12 @@
 #!/bin/sh
+# installs fnm (Fast Node Manager)
+curl -fsSL https://fnm.vercel.app/install | bash
+# download and install Node.js
+fnm use --install-if-missing 20
+# verifies the right Node.js version is in the environment
+node -v # should print `v20.15.0`
+# verifies the right NPM version is in the environment
+npm -v # should print `10.7.0`
 
 unzip gradio-image-prompter-visible-boxes-main.zip
 cd gradio-image-prompter-visible-boxes-main