Merge pull request #75 from xav-db/master

adding helix-db to readme

Author: wujunze

README.md

@@ -167,6 +167,7 @@ See also [Friends of Rust](https://prev.rust-lang.org/en-US/friends.html) (Organ
 ### Database
 
 * [indradb](https://crates.io/crates/indradb) — Rust based graph database [<img src="https://api.travis-ci.org/indradb/indradb.svg?branch=master">](https://travis-ci.org/indradb/indradb)
+* [HelixDB](https://github.com/HelixDB/helix-db) — An open-source graph-vector database written in Rust [<img src="https://raw.githubusercontent.com/HelixDB/helix-db/main/assets/full_logo.png">](https://raw.githubusercontent.com/HelixDB/helix-db/main/assets/full_logo.png)
 * [noria](https://crates.io/crates/noria) — Dynamically changing, partially-stateful data-flow for web application backends [<img src="https://api.travis-ci.org/mit-pdos/noria.svg?branch=master">](https://travis-ci.org/mit-pdos/noria)
 * [PumpkinDB](https://github.com/PumpkinDB/PumpkinDB) — an event sourcing database engine [<img src="https://api.travis-ci.org/PumpkinDB/PumpkinDB.svg?branch=master">](https://travis-ci.org/PumpkinDB/PumpkinDB)
 * [seppo0010/rsedis](https://github.com/seppo0010/rsedis) — A Redis reimplementation in Rust [<img src="https://api.travis-ci.org/seppo0010/rsedis.svg?branch=master">](https://travis-ci.org/seppo0010/rsedis)