Add `shubham0204/pq.rs`, a Rust implementation of `pq.py`, as a community resource in `README.md`

[shubham0204]

I wanted to learn how product quantization works, and this repository provided excellent code to understand how it works. As I had been learning Rust for a few months now, I decided to re-write the pq.py script in Rust to understand each step thoroughly by self-implementation. Here's the repository containing the Rust code: shubham0204/pq.rs.

The following steps are have to be taken in order to complete the project:

1. Complete README.md and add a small usage sample of the Rust API
2. Prepare a crate and upload it to crates.io

Do let me know if the repository can be included as a community resource. Just like me, many other learners would like to learn implementation of product quantization in languages other than Python, and building a section where implementations in other languages would be of great help. Moreover, I'm also working on a detailed blog which will explain product-quantization from first-concepts and with a Rust implementation.

[matsui528]

@shubham0204

Great! Please include the link to https://github.com/matsui528/nanopq in your README.

Let me know when you finished the project. I'll add a link to your repository in my README.