docs: Fix opendal rust core's README not align with new vision #2349

Job	Run time
build_all_features	5m 3s
build_all_platforms (ubuntu-latest)	2m 30s
build_all_platforms (macos-latest)	2m 25s
build_default_features (ubuntu-latest)	47s
build_all_platforms (windows-latest)	4m 59s
build_under_wasm	55s
build_default_features (macos-latest)	46s
build_default_features (windows-latest)	1m 38s
check_clippy	3m 51s
check_docs	3m 37s
check_msrv	38s
unit	7m 2s
	34m 11s

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