Add module-level docs for Curve #51046

Job	Run time
build (windows-latest)	1m 6s
check-bevy-internal-imports	5s
build (ubuntu-latest)	1m 19s
check-doc	1m 19s
check-missing-examples-in-docs	32s
ci	1m 16s
build (macos-latest)	1m 19s
miri	1m 19s
toml	1m 19s
typos	7s
check-missing-features-in-docs	30s
markdownlint	1m 11s
check-compiles	1s
check-compiles-no-std	1s
msrv	1s
build-wasm	1s
build-wasm-atomics	1s
	11m 27s

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