Move README to jemallocator

Signed-off-by: Jay Lee <BusyJayLee@gmail.com>

README.md

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+jemallocator/README.md

jemallocator/README.md

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+# tikv-jemallocator
+
+[![ci]][github actions] [![Latest Version]][crates.io] [![docs]][docs.rs]
+
+This project is the successor of [jemallocator](https://github.com/gnzlbg/jemallocator).
+
+The project is also published as `jemallocator` for historical reasons. The two crates are the same except names. For new projects, it's recommended to use `tikv-xxx` versions instead.
+
+> Links against `jemalloc` and provides a `Jemalloc` unit type that implements
+> the allocator APIs and can be set as the `#[global_allocator]`
+
+## Overview
+
+The `jemalloc` support ecosystem consists of the following crates:
+
+* `tikv-jemalloc-sys`: builds and links against `jemalloc` exposing raw C bindings to it.
+* `tikv-jemallocator`: provides the `Jemalloc` type which implements the
+  `GlobalAlloc` and `Alloc` traits. 
+* `tikv-jemalloc-ctl`: high-level wrapper over `jemalloc`'s control and introspection
+  APIs (the `mallctl*()` family of functions and the _MALLCTL NAMESPACE_)'
+
+## Documentation
+
+* [Latest release (docs.rs)][docs.rs]
+
+To use `tikv-jemallocator` add it as a dependency:
+
+```toml
+# Cargo.toml
+[dependencies]
+
+[target.'cfg(not(target_env = "msvc"))'.dependencies]
+tikv-jemallocator = "0.5"
+```
+
+To set `tikv_jemallocator::Jemalloc` as the global allocator add this to your project:
+
+```rust
+# main.rs
+#[cfg(not(target_env = "msvc"))]
+use tikv_jemallocator::Jemalloc;
+
+#[cfg(not(target_env = "msvc"))]
+#[global_allocator]
+static GLOBAL: Jemalloc = Jemalloc;
+```
+
+And that's it! Once you've defined this `static` then jemalloc will be used for
+all allocations requested by Rust code in the same program.
+
+## Platform support
+
+The following table describes the supported platforms: 
+
+* `build`: does the library compile for the target?
+* `run`: do `tikv-jemallocator` and `tikv-jemalloc-sys` tests pass on the target?
+* `jemalloc`: do `tikv-jemalloc`'s tests pass on the target?
+
+Tier 1 targets are tested on all Rust channels (stable, beta, and nightly). All
+other targets are only tested on Rust nightly.
+
+| Linux targets:                      | build     | run     | jemalloc     |
+|-------------------------------------|-----------|---------|--------------|
+| `aarch64-unknown-linux-gnu`         | ✓         | ✓       | ✗            |
+| `powerpc64le-unknown-linux-gnu`     | ✓         | ✓       | ✗            |
+| `x86_64-unknown-linux-gnu` (tier 1) | ✓         | ✓       | ✓            |
+| **MacOSX targets:**                 | **build** | **run** | **jemalloc** |
+| `x86_64-apple-darwin` (tier 1)      | ✓         | ✓       | ✗            |
+
+## Features
+
+The `tikv-jemallocator` crate re-exports the [features of the `tikv-jemalloc-sys`
+dependency](https://github.com/tikv/jemallocator/blob/master/jemalloc-sys/README.md).
+
+## License
+
+This project is licensed under either of
+
+ * Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
+   http://www.apache.org/licenses/LICENSE-2.0)
+ * MIT license ([LICENSE-MIT](LICENSE-MIT) or
+   http://opensource.org/licenses/MIT)
+
+at your option.
+
+## Contribution
+
+Unless you explicitly state otherwise, any contribution intentionally submitted
+for inclusion in `tikv-jemallocator` by you, as defined in the Apache-2.0 license,
+shall be dual licensed as above, without any additional terms or conditions.
+
+[Latest Version]: https://img.shields.io/crates/v/tikv-jemallocator.svg
+[crates.io]: https://crates.io/crates/tikv-jemallocator
+[docs]: https://docs.rs/tikv-jemallocator/badge.svg
+[docs.rs]: https://docs.rs/tikv-jemallocator/
+[ci]: https://github.com/tikv/jemallocator/actions/workflows/main.yml/badge.svg
+[github actions]: https://github.com/tikv/jemallocator/actions