chore: add general usage message to --help message (#3500)

packages/cli/src/config/config.ts

@@ -53,6 +53,11 @@ interface CliArgs {
 
 async function parseArguments(): Promise<CliArgs> {
   const argv = await yargs(hideBin(process.argv))
+    .scriptName('gemini')
+    .usage(
+      '$0 [options]',
+      'Gemini CLI - Launch an interactive CLI, use -p/--prompt for non-interactive mode',
+    )
     .option('model', {
       alias: 'm',
       type: 'string',