Q:

How to launch the julia interpreter with arguments in juno? 

How can I launch the julia interpreter with arguments (-p 4 for workers), in the juno plugin for atom? 
For example in the command line, you call:
julia -p 4
and you start the julia interpreter with 4 workers. 

A:

This is not an answer how to do it in Juno, but a general hint: you can also manage the workers within a Julia process.  Here is an example within the REPL
julia> addprocs(4)
4-element Array{Int64,1}:
 2
 3
 4
 5

julia> rmprocs(2)
:ok

julia> workers()
3-element Array{Int64,1}:
 3
 4
 5

