[docs] Rust以外の１つの言語でのコア機能追加実装はしない方針であることを明記 (#632) #2086

Job	Run time
actionlint	26s
shellcheck	13s
validate-cargo-lock	33s
build-and-test-java-api (windows-latest)	8m 27s
build-and-test-java-api (macos-latest)	8m 7s
build-and-test-java-api (ubuntu-latest)	3m 56s
build-and-test-python-api (windows-latest)	12m 3s
build-and-test-python-api (macos-latest)	7m 18s
build-unix-cpp-example (macos-latest, osx-x64-cpu-cpp-shared)	4m 13s
build-and-test-python-api (ubuntu-latest)	4m 43s
build-unix-cpp-example (ubuntu-latest, linux-x64-cpu-cpp-shared)	2m 48s
build-windows-cpp-example	7m 38s
c-header	1m 54s
rust-integration-test-strategy-matrix	3s
rust-lint	3m 26s
rust-unit-test	5m 8s
rust-integration-test (windows-2019, directml)	4m 53s
rust-integration-test (macos-11)	4m 28s
rust-integration-test (ubuntu-20.04)	2m 5s
	1h 22m 22s

Provide feedback