add missing type description

cli/args.js

@@ -89,6 +89,7 @@ const args = require("yargs")
 	.options("back-end", { description: "Back-end to use" })
 	.choices("back-end", ["jsdom", "puppeteer", "webdriver-chromium", "webdriver-gecko", "puppeteer-firefox", "playwright-firefox", "playwright-chromium"])
 	.options("browser-server", { description: "Server to connect to (puppeteer only for now)" })
+	.string("browser-server")
 	.options("browser-headless", { description: "Run the browser in headless mode (puppeteer, webdriver-gecko, webdriver-chromium)" })
 	.boolean("browser-headless")
 	.options("browser-executable-path", { description: "Path to chrome/chromium executable (puppeteer, webdriver-gecko, webdriver-chromium)" })