Add pg dependency

[sjoerdsmink]

The package pg is a dependency which is needed. To put this in the devDependencies, but mentioning in the readme that it's required seems contradicting. Also updated the TypeScript reference to pg-pool instead of an any.

[darrachequesne]

That's a fair point. One potential use case is to allow the user to provide another PostgreSQL client: in the case of the Redis adapter for example, you can provide a client from redis or ioredis.

Also, it would mean that we force the user to use pg@^8.0.0, which may not be great. What do you think?

[sjoerdsmink]

Still if you want to support other pool clients, you need to define the types. Because otherwise this.pool.connect() and this.pool.query would crash. The whole code expects pg-node's pool in this argument, e.g. pool.connect() should return a client, which can have client.query(), client.removeAllListeners(), client.release(), client.on(). Don't think there's any other package that does exactly that :)

pg@^8.0.0 means pg version 8.x.x. In case a user wants another major version, npm or yarn will install the pg dependency in node_modules/@socket.io/postgres-adapter/node_modules/pg

[darrachequesne]

Well that makes sense! Merged as d6d74d5, thanks 👍