docs: update README and blog for version 0.4.0 release, highlighting new features and improvements

docs/md_v2/blog/index.md

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+# Crawl4AI Blog
+
+Welcome to the Crawl4AI blog! Here you'll find detailed release notes, technical deep dives, and news about the project.
+
+## Latest Release
+
+### [0.4.0 - Major Content Filtering Update](releases/0.4.0.md)
+*December 1, 2024*
+
+Introducing significant improvements to content filtering, multi-threaded environment handling, and user-agent generation. This release features the new PruningContentFilter, enhanced thread safety, and improved test coverage.
+
+[Read full release notes →](releases/0.4.0.md)
+
+## Project History
+
+Want to see how we got here? Check out our [complete changelog](https://github.com/unclecode/crawl4ai/blob/main/CHANGELOG.md) covering all previous versions and the evolution of Crawl4AI.
+
+## Categories
+
+- [Technical Deep Dives](/blog/technical) - Coming soon
+- [Tutorials & Guides](/blog/tutorials) - Coming soon
+- [Community Updates](/blog/community) - Coming soon
+
+## Stay Updated
+
+- Star us on [GitHub](https://github.com/unclecode/crawl4ai)
+- Follow [@unclecode](https://twitter.com/unclecode) on Twitter
+- Join our community discussions on GitHub