Update README.md file for Sprint 4

[sandyl289]

🏁 Setups

• [x] Add "Sprint 4: Effort Table" skeleton in README.md file
• [x] Add hyperlink to wiki page "Sprint 4: Report"

✅ TO DO: (before submission)

• [x] Update Sprint 4 Effort (hours) column in Overview Table of the README.md file
• [x] Update Contributions column of the Sprint 4: Effort Table to be the same as the wiki page [Effort Table 🏋️]
• [x] Update Efforts (hours) column of the Sprint 4: Effort Table to be the same as the wiki page [Effort Table 🏋️]

[sandyl289]

Done!

[sandyl289]

I wonder if we'll need a README.md on the android branch

• [x] Copy README.md from main & paste it to android branch

[sandyl289]

Done!