Add PostgreSQL hacking

A curated list of awesome PostgreSQL hacking resources.

Author: zhjwpku

readme.md

@@ -582,6 +582,7 @@
 - [RethinkDB](https://github.com/d3viant0ne/awesome-rethinkdb#readme)
 - [TinkerPop](https://github.com/mohataher/awesome-tinkerpop#readme) - Graph computing framework.
 - [PostgreSQL](https://github.com/dhamaniasad/awesome-postgres#readme) - Object-relational database.
+	- [Hacking](https://github.com/pghacking/awesome-postgres-hacking#readme) - PostgreSQL hacking resources.
 - [CouchDB](https://github.com/quangv/awesome-couchdb#readme) - Document-oriented NoSQL database.
 - [HBase](https://github.com/rayokota/awesome-hbase#readme) - Distributed, scalable, big data store.
 - [NoSQL Guides](https://github.com/erictleung/awesome-nosql-guides#readme) - Help on using non-relational, distributed, open-source, and horizontally scalable databases.