Update README.md with TypeScript testing info

PER-9318: Write healthcheck test (webclient functional test)

js/README.md

@@ -3,3 +3,13 @@
 The `js` directory contains the in-development replacement for the Permanent Functional Test. It uses end-to-end testing via Cypress to test functionality rather than hitting the API directly.
 
 Currently it exists in a subdirectory since the plan is to eventually completely replace the Python project in this repository, rather than make a new one.
+
+## Setup
+
+Run `npm install` to install dependencies.
+
+## Running Tests
+
+To run headless tests, simply run `npm start`.
+
+To run tests in the Cypress UI, run `npm run cypress:open`.