Document how to debug unit tests in VSCode (#2297)

## Which problem is this PR solving?
 Resolve #2118 

## Description of the changes
- Added a launch json in the README.md which explains how to set the
debugger of vscode to test unit tests with jest.

## How was this change tested?
-  Proof of work was present in the comment thread of the issue #2118 

## Checklist
- [x] I have read
https://github.com/jaegertracing/jaeger/blob/master/CONTRIBUTING_GUIDELINES.md
- [x] I have signed all commits
- [] I have added unit tests for the new functionality
- [] I have run lint and test steps successfully
  - for `jaeger`: `make lint test`
  - for `jaeger-ui`: `yarn lint` and `yarn test`

---------

Signed-off-by: RISHIKESHk07 <rishikeshkuppala@gmail.com>
Signed-off-by: Yuri Shkuro <github@ysh.us>
Co-authored-by: Yuri Shkuro <github@ysh.us>

README.md

@@ -104,6 +104,37 @@ Here are some steps to follow:
 
 See the [configuration guide](https://www.jaegertracing.io/docs/latest/frontend-ui/) for details on configuring Google Analytics tracking, menu customizations, and other aspects of UI behavior.
 
+## Debug unit tests from Vscode (launch.json file given below)
+
+```javascript
+{
+    // Use IntelliSense to learn about possible attributes.
+    // Hover to view descriptions of existing attributes.
+    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "type": "node",
+            "request": "launch",
+            "name": "Jest: current file",
+            "skipFiles": [
+                "<node_internals>/**"
+            ],
+            "program": "${workspaceFolder}/node_modules/.bin/jest",
+            "args": [
+                "${file}"
+            ],
+            "console": "integratedTerminal",
+            "cwd": "${workspaceFolder}/packages/jaeger-ui",
+        },
+
+    ]
+}
+
+```
+
+See the [configuration guide](https://www.jaegertracing.io/docs/latest/frontend-ui/) for details on configuring Google Analytics tracking, menu customizations, and other aspects of UI behavior.
+
 ## License
 
 [Apache 2.0 License](./LICENSE).