[README] Update installation doc

[chengyupku]

This pull request primarily removes two example scripts related to distributed all-gather GEMM operations, and makes minor improvements to the installation documentation. The documentation changes clarify installation steps and usage instructions for users, while the code deletions clean up the repository by removing outdated or redundant examples.

Documentation improvements:

• Added an "Installation" section to the README.md with a link to the detailed installation guide for easier onboarding.
• Simplified and clarified example usage and verification steps in docs/get_started/Installation.md to make instructions more direct and user-friendly. [1] [2]

Codebase cleanup:

• Removed the entire examples/distributed/example_allgather_gemm_overlapped_fast_sync.py script, which contained an advanced distributed GEMM example using TileScale and PyTorch.
• Removed the entire examples/distributed/example_allgather_gemm_overlapped_persistent.py script, another distributed GEMM example with persistent kernels and performance benchmarking.

[github-actions]

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