Update Documentation and Docsite

[alronlam]

What does this PR do?

• Add overall summary in index.qmd (the main page). Removed the about and progress pages as those are irrelevant now.
• Minor refactors: moved .qmd files into the docs/ subdir to lessen the amount of files in the root dir.
• Update README.md to contain updated instructions for extra data set-up (DHS and EOG).

Where should the reviewers start?

• docs/index.qmd This is the main addition. The docsite has already been uploaded, so you can check it out here: https://thinkingmachines.github.io/unicef-ai4d-poverty-mapping/
• README.md

Addresses Issue: #194, #95 , and #195.

Also verified that Issue #185 is already resolved on this branch (addressed in one of the refactors in previous PRs).

[alronlam]

Closes Issues #194 , #195 and #95 .

Also verified Issue #185 is ok as of this PR merge. (Actual fix was likely in a previous PR when requirements files were fixed).