Add hints to use macro packages for new users

[bkamins]

Users asked to give a hint that macro-packages can be easier to use for newcomers in the opening page of DataFrames.jl manual near its top (so that it is easily discoverable).

@nalimilan, @pdeffebach, @jkrumbiegel - I have proposed something, but I am not sure if the wording is best. Can you please comment? (I think that good wording here is important) Thank you!

Also I mention only DataFramesMeta.jl as I did not want to introduce additional user confusion (i.e. that they need to make choices between DataFramesMeta.jl and DataFrameMacros.jl). But maybe it is better to mention both. I am open for suggestions.
(they are both mentioned below in data wrangling section)

[pdeffebach]

I think this looks good, thanks!

[jkrumbiegel]

One the one hand I'm ok with the text as it is, on the other you might add something like "or one of the other convenience packages" or so and just intra-link to the section where they are shown. Often people just stick with what they encounter first, so I personally like laying out the options early. Unless you want to endorse DataFramesMeta as the macro-arm of DataFrames, which you can of course do and might be a good decision, too, from an ecosystem building perspective. I'm happy if people find something that works for them in the Julia ecosystem, my only worry regarding DataFrameMacros was always that it would mostly be disregarded because it seems not to be the "official" package (without understanding anything about the differences), not because it's not good.

[bkamins]

Unless you want to endorse DataFramesMeta

I do not want to endorse a single package. I will add a sentence you propose with the link to the section.

[jkrumbiegel]

Sounds good, thank you!

[bkamins]

Thank you!