Enhancement: Add helpful (error) message when trying to add scalar + array in 1.0+

[elcritch]

I'm trying to pickup the Julia 1.0 syntax differences. One major gotcha for me was the removal of the convenience scalar +/- array functions in favor of the explicit .+ forms. This surprised me and took me a bit to figure out. It's noted in the NEWS.md for the 0.7 release it's not in the 1.0 NEWS.md nor in the early sections of the Julia manual.

Would it be possible to add a warning or a helpful compiler message in the repl along the lines "you might try .+"? Many people picking up Julia will be coming from Python or Matlab where I believe the default is to broadcast addition/sum. It's a small matter, but if in the first 5 minutes someone is trying out Julia and can't figure out how to add 4 to their array it could be very frustrating.

Alternately, ensuring it's clearly stated the first time array operations are introduced in the manual might work just as well.

julia> 4 + [ 1.0, 2.0 ]
ERROR: MethodError: no method matching +(::Int64, ::Array{Float64,1})
Closest candidates are:
+(::Any, ::Any, ::Any, ::Any...) at operators.jl:502
+(::T<:Union{Int128, Int16, Int32, Int64, Int8, UInt128, UInt16, UInt32, UInt64, UInt8}, ::T<:Union{Int128, Int16, Int32, Int64, Int8, UInt128, UInt16, UInt32, UInt64, UInt8}) where T<:Union{Int128, Int16, Int32, Int64, Int8, UInt128, UInt16, UInt32, UInt64, UInt8} at int.jl:53
+(::Union{Int16, Int32, Int64, Int8}, ::BigInt) at gmp.jl:456
...
Stacktrace:
[1] top-level scope at none:0

julia> 4 .+ [ 1.0, 2.0 ]
2-element Array{Float64,1}:
5.0
6.0

[JeffBezanson]

Related: #29266

[laborg]

The error message has been implemented in the meantime:

julia> 4 + [ 1.0, 2.0 ]
ERROR: MethodError: no method matching +(::Int64, ::Vector{Float64})
For element-wise addition, use broadcasting with dot syntax: scalar .+ array