Readme has a broken link. Needs to be updated with correct file path

[gatlee21]

The Readme in arduino-ide/arduino-ide-extension/ has a broken path link.

To Reproduce
Steps to reproduce the behavior:

1. Go to arduino-ide/arduino-ide-extension/README.md
2. Scroll down to Monitor Service
3. Click on the link src/node/monitor-service-impl.ts
4. It takes you to a 404 page not found

Expected behavior
I believe this file was moved into another folder named monitor, making the correct path for this file here src/node/monitor/monitor-service-impl.ts

Proposed resolution
Change this path src/node/monitor-service-impl.ts
To this src/node/monitor/monitor-service-impl.ts

[yash-markad]

issue has been solved
#467 (comment)

[fstasi]

Confirm this is solved. Thanks!