chore: checkpoint before Python removal

vendor/icu_properties/README.md

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+# icu_properties [![crates.io](https://img.shields.io/crates/v/icu_properties)](https://crates.io/crates/icu_properties)
+
+<!-- cargo-rdme start -->
+
+Definitions of [Unicode Properties] and APIs for
+retrieving property data in an appropriate data structure.
+
+This module is published as its own crate ([`icu_properties`](https://docs.rs/icu_properties/latest/icu_properties/))
+and as part of the [`icu`](https://docs.rs/icu/latest/icu/) crate. See the latter for more details on the ICU4X project.
+
+APIs that return a `CodePointSetData` exist for binary properties and certain enumerated
+properties.
+
+APIs that return a `CodePointMapData` exist for certain enumerated properties.
+
+## Examples
+
+### Property data as `CodePointSetData`s
+
+```rust
+use icu::properties::{CodePointSetData, CodePointMapData};
+use icu::properties::props::{GeneralCategory, Emoji};
+
+// A binary property as a `CodePointSetData`
+
+assert!(CodePointSetData::new::<Emoji>().contains('🎃')); // U+1F383 JACK-O-LANTERN
+assert!(!CodePointSetData::new::<Emoji>().contains('木')); // U+6728
+
+// An individual enumerated property value as a `CodePointSetData`
+
+let line_sep_data = CodePointMapData::<GeneralCategory>::new()
+    .get_set_for_value(GeneralCategory::LineSeparator);
+let line_sep = line_sep_data.as_borrowed();
+
+assert!(line_sep.contains('\u{2028}'));
+assert!(!line_sep.contains('\u{2029}'));
+```
+
+### Property data as `CodePointMapData`s
+
+```rust
+use icu::properties::CodePointMapData;
+use icu::properties::props::Script;
+
+assert_eq!(CodePointMapData::<Script>::new().get('🎃'), Script::Common); // U+1F383 JACK-O-LANTERN
+assert_eq!(CodePointMapData::<Script>::new().get('木'), Script::Han); // U+6728
+```
+
+[`ICU4X`]: ../icu/index.html
+[Unicode Properties]: https://unicode-org.github.io/icu/userguide/strings/properties.html
+
+<!-- cargo-rdme end -->
+
+## More Information
+
+For more information on development, authorship, contributing etc. please visit [`ICU4X home page`](https://github.com/unicode-org/icu4x).