Add guide for accessing Copilot Workspace on Android

[Mike-FreeAI]

Updates the README.md file and the images/repo-task-timeline-representation.png file to include a new guide on accessing Copilot Workspace on Android devices.

• Adds a new section titled "Accessing Copilot Workspace on Android" to README.md which:
  • Provides steps to navigate to the Copilot Workspace dashboard on a mobile browser.
  • Details the process to add Copilot Workspace to the home screen for easy access.
  • Mentions the PWA support for a native app-like experience on Android.
  • Notes that access is exclusively available to GitHub Next subscribers.
• Includes an image in the guide by changing images/repo-task-timeline-representation.png, enhancing the visual representation of the guide.

---

For more details, open the Copilot Workspace session.

[dsyme]

@lostintangent These look good but I'm aware we still have reports of PWA bug on Android?

[lostintangent]

I went ahead and added these changes to the "tips & tricks" doc, since that was the more appropriate place for them. That said, I'll close this PR in place of that change. Thanks @MrDevel0per!