Missing instructions to setup db authentication method

[PRijnbeek]

Needs to be added with a new page here: https://github.com/OHDSI/ArachneNodeAPI/wiki

Find here an example of using an external postgres db on the host for authentication.

datanode-example.zip

Note i use port 81 because Atlas is running on port 80 on the same machine

You need to setup a database with the following information:

A hash to use for the word password for testing:
$2a$10$36vcvLu3wqZ7NwAcRJg3L.pfr6Kc.36X6BEnbpEKJ1RnsWXOmBdjC

I think it is better to use a db outside of the docker so it persists also after data node updates

[alex-odysseus]

Duplicates #43