After some cleaning on my computer I run Julia 1.0 and have
ERROR: ArgumentError: Package IJulia not found in current path:
- Run `Pkg.add("IJulia")` to install the IJulia package.
 require(::Module, ::Symbol) at ./loading.jl:817
Pkg.add was removed from REPL is this error just legacy of previous versions? Or this error is left for Jupyter/other environments use?
What do you mean?
import Pkg; Pkg.add("IJulia")
still works. The error message was tweaked here: https://github.com/JuliaLang/julia/pull/28555
Thank you for explanation, I wrongly understood someone words that they removed Pkg from REPL, when they just moved it to some Basic (?) library. I try to fallow changes in the version 1.0, still I miss something.
I think the error should say:
Run "Using Pkg; Pkg.add("IJulia")" to install the IJulia package.
It will be changed to that in Julia v1.0.1.