docs for columns linkTo helper

[pxpm]

docs for Laravel-Backpack/CRUD#5317

[tabacitu]

Pedro I like the text you wrote, but I didn't like that it was crowded inside the wrapper docs. I moved it outside in its own section, I think that will be clearer... and will give us the option of linking to this feature in particular.

[tabacitu]

This is excellent! Ready to go from my point of view, take it away @pxpm / @promatik !