Clarification on thread-safety

The docs have a very brief page on thread-safety: https://jdbc.postgresql.org/documentation/head/thread.html

It states, pretty categorically: "The PostgreSQL™ JDBC driver is not thread safe".

However, it's common to want to open new connections from multiple threads.

A cursory look at `PGSimpleDataSource` and `org.postgresql.Driver.connect` suggests both of these methods are thread safe.

Perhaps this is an "obvious" level of thread-safety, but I think the doc page spelling it out would save other paranoid folks like me some time.