add brief instructions on how to run e2e tests locally

e2e/RUNNING_LOCALLY.md

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+To run e2e tests locally:
+
+1. start grunt in e2e folder - `npx grunt server`
+2. edit Procfile, remove the web task (it is for serving a static bundle which we don't want in order not to lose live-reload support)
+3. start mongo, redis, elastic services
+4. create a virtual environment in e2e/server, install dependencies and start honcho
+5. run `TZ="Australia/Sydney" npm run cypress-ui` in `e2e` folder. Notice we set a timezone environment variable before launching cypress. Some tests depend on a timezone and would fail it timezone wasn't set.
+