Update README.md : Add SummaryTube in AI tool list

[ritwickhalder]

Added SummaryTube in list of AI tools

SummaryTube helps you save time and create AI powered smart video summaries for any YouTube video for FREE. Generate video summaries, key moments and transcripts for any YouTube video easily. Users can promote Youtube content for free by generating and sharing beautiful video summaries with users. Browse easily through your saved video summaries anytime in your account. Use chrome extension to summarize directly on Youtube. Get key insights & transcripts from youtube video, Q&A & save/share summaries easily.