Auto-import Prelude in PSCI

[chexxor]

Newcomers to PureScript expect to be able to do

$ pulp init
$ pulp psci
> 1 + 1
2

Pulp is a good place for user-convenience things like this. Perhaps pulp init could add "import Prelude" to a .psci file, which is executed to initialize the psci environment.

I recall a .psci file being supported by psci in the past, but it's been removed, I believe.

[chexxor]

Made an issue to re-add the .psci file support: purescript/purescript#2734