Improve examples in the manual in basics.md

[bkamins]

Small improvements based on user feedback

[nalimilan]

But this is slower as it recreates the array, right?

[bkamins]

Yes:

julia> length(x)
1000000

julia> @time [a in [1, 5, 601] for a in x];
  0.066654 seconds (1.06 M allocations: 80.224 MiB, 10.75% gc time, 32.44% compilation time)

julia> in.(x, Ref([1, 5, 601]));

julia> @time in.(x, Ref([1, 5, 601]));
  0.002442 seconds (8 allocations: 126.547 KiB)

julia> @time in([1, 5, 601]).(x);
  0.002134 seconds (8 allocations: 126.531 KiB)

I will add this comment.

[bkamins]

added

[bkamins]

Thank you!