Fix requirements.md link and improve PostgreSQL commands

 - Point requirements.md link to the correct location

 - Link to gitlab installation.md document instead of github

 - Use psql command switch to run specified SQL commands for creation of user and database permissions.
    -  Instead of requiring a comment like `# Do not type the 'template1=#', this is part of the prompt` it may be easier to just use the command switch with `psql` to execute the SQL commands.


*forgot [ci skip] :(*

See merge request !3176