Fix: Corrected dead links in README

[jonathan-d-nguyen]

Summary

This Pull Request corrects dead links found in the project's main documentation.

Details

This Pull Request fixes several dead links (404s) found within the Further info section of the README.md.

The following links were updated:

• Complete User Guide: Corrected link to the new location of the full user documentation.
• CLI tools: Updated the link pointing to the command-line interface tools documentation.
• Managing multiple Projects: Updated the link to the correct resource on handling multi-project setups.
• Importing data from OpenAI/Claude Projects: Corrected the link for data import guides from external projects.

Verification

I have manually tested all four updated links and confirmed that they resolve correctly and point to the intended documentation pages.

[CLAassistant]

All committers have signed the CLA.

[phernandez]

Thanks @jonathan-d-nguyen !