Add "Related Projects" section to README

Hi! 👋

First of all, thank you for creating opensrc — it's been a great inspiration for my work.

I built llms-furl, a tool that takes the same Unix-philosophy approach but for llms-full.txt files. While opensrc fetches package source code for agent context, llms-furl splits monolithic LLM documentation into a searchable filesystem tree.

I was wondering if you'd be open to adding a "Related Projects" section to the README to mention llms-furl. I think it could be helpful for users who are looking for complementary tools in this space.

If you'd prefer not to include it, or if there's a different format you'd like, I'm happy to adjust. Just let me know!

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Changes:

Added a "Related Projects" section before the License section