Update README.md

add link to main README>md

Author: ianscrivener

README.md

@@ -17,6 +17,9 @@ This package provides:
 
 Documentation is available at [https://abetlen.github.io/llama-cpp-python](https://abetlen.github.io/llama-cpp-python).
 
+Detailed MacOS Metal GPU install documentation is available at [docs/macos_install.md](docs/macos_install.md)
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 ## Installation from PyPI (recommended)
 
 Install from PyPI (requires a c compiler):