Add Pyslang homepage content from README, add navbar #2390

Job	Run time
build (clang-sanitize, ubuntu-latest)	45m 31s
build (gcc-release, ubuntu-24.04-arm)	9m 26s
build (gcc-11-release, ubuntu-latest)	9m 3s
build (gcc-debug-shared, ubuntu-latest)	8m 57s
build (gcc-debug-noexcept, ubuntu-latest)	8m 58s
build (macos-release, macos-latest)	7m 33s
build (win64-release, windows-latest)	14m 0s
build (win64-debug-shared, windows-latest)	11m 32s
build (win64-debug-noexcept, windows-latest)	10m 1s
	2h 5m 1s

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