Update mapping.md

[manjitapandey]

updated mapper's page documentation

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

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

Related Issue

Example: Related #921

Describe this PR

• updated text mapper frontend to mapper page
• Updated documentations based on recent mapper's page improvement

Screenshots

Please provide screenshots of the change.

Alternative Approaches Considered

Did you attempt any other approaches that are not documented in code?

Review Guide

Notes for the reviewer. How to test this change?

Checklist before requesting a review

• 📖 Read the FMTM Contributing Guide: https://github.com/hotosm/fmtm/blob/main/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?