Update readme landing page screenshot location

[spwoodcock]

What type of PR is this? (check all applicable)

• 🍕 Feature
• 🐛 Bug Fix
• 📝 Documentation
• 🧑‍💻 Refactor
• ✅ Test
• 🤖 Build or CI
• ❓ Other (please specify)

Describe this PR

• I think during a refactor to us mkdocs, the screenshot.jpg image in root was moved to docs/images/.

• The readme currently shows:

  

• I updated the link to reference the new location.

Checklist before requesting a review

• 📖 Read the Tasking Manager Contributing Guide: https://github.com/hotosm/tasking-manager/blob/develop/docs/developers/contributing.md
• 📖 Read the HOT Code of Conduct: https://docs.hotosm.org/code-of-conduct
• 👷‍♀️ Create small PRs. In most cases, this will be possible.
• ✅ Provide tests for your changes.
• 📝 Use descriptive commit messages.
• 📗 Update any related documentation and include any relevant screenshots.

[optional] What gif best describes this PR or how it makes you feel?

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
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See analysis details on SonarCloud