Adds four xberg-io libraries with native Java bindings (Rust core, MIT), placed alphabetically:

• Document Processing — xberg (document intelligence, 97+ formats + OCR) and html-to-markdown
• Web Crawling — crawlberg
• Machine Learning — liter-llm (universal LLM client, 142+ providers)

Summary by cubic

Adds four xberg-io libraries with native Java bindings to the README, alphabetized in their categories. Adds xberg and html-to-markdown (Document Processing), crawlberg (Web Crawling), and liter-llm (LLM frameworks) with cleaned-up descriptions covering Java bindings, Markdown conversion, optional browser rendering, and a unified LLM client.

^{Written for commit 0ffa6e9. Summary will update on new commits.}