Clarify Playwright setup README and add note to .env_example (#3336)

Co-authored-by: Benjamin Lu <templu1107@proton.me>

.env_example

@@ -1,4 +1,5 @@
 # Local development playwright target
+# Note: Don't add a trailing / after the port
 PLAYWRIGHT_TEST_URL=http://localhost:5173
 # PLAYWRIGHT_TEST_URL=http://localhost:8188
 

browser_tests/README.md

@@ -9,15 +9,26 @@ If `TEST_COMFYUI_DIR` in `.env` isn't set to your `(Comfy Path)/ComfyUI` directo
 
 ## Setup
 
-Clone <https://github.com/Comfy-Org/ComfyUI_devtools> to your `custom_nodes` directory.
-ComfyUI_devtools adds additional API endpoints and nodes to ComfyUI for browser testing.
+### ComfyUI devtools
+Clone <https://github.com/Comfy-Org/ComfyUI_devtools> to your `custom_nodes` directory.  
+_ComfyUI_devtools adds additional API endpoints and nodes to ComfyUI for browser testing._
 
+### Node.js & Playwright Prerequisites
 Ensure you have Node.js v20 or later installed. Then, set up the Chromium test driver:
-
 ```bash
 npx playwright install chromium --with-deps
 ```
 
+### Environment Variables
+Ensure the environment variables in `.env` are set correctly according to your setup. 
+
+The `.env` file will not exist until you create it yourself.
+
+A template with helpful information can be found in `.env_example`.
+
+### Multiple Tests
+If you are running Playwright tests in parallel or running the same test multiple times, the flag `--multi-user` must be added to the main ComfyUI process.
+
 ## Running Tests
 
 There are two ways to run the tests:
@@ -34,8 +45,6 @@ There are two ways to run the tests:
    ```
    This opens a user interface where you can select specific tests to run and inspect the test execution timeline.
 
-   To run the same test multiple times in Playwright's UI mode, you must launch the main ComfyUI process with the `--multi-user` flag.
-
    ![Playwright UI Mode](https://github.com/user-attachments/assets/6a1ebef0-90eb-4157-8694-f5ee94d03755)
 
 ## Screenshot Expectations