Update Readme instructions to include devcontainer instructions

[oscar-edomex]

Maybe we should update this file to have instructions on using devcontainers now that OpenSourceFellows/map-dashboard#162 has been merged. This is the way I imagine most people will want to run the app for development.

Originally posted by @DietBepis1 in https://github.com/OpenSourceFellows/map-dashboard/pull/163#discussion_r2505558714

[coderabbitai]

📝 CodeRabbit Plan Mode

Generate an implementation plan and prompts that you can use with your favorite coding agent.

• Create Plan

Examples

• Example 1
• Example 2

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You can configure auto-planning by selecting labels in the issue_enrichment configuration.

To disable automatic issue enrichment, add the following to your .coderabbit.yaml:

issue_enrichment:
  auto_enrich:
    enabled: false

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